From db36990774f18d11a7b3121fb91fc5eb049ea87e Mon Sep 17 00:00:00 2001
From: Athan Reines <kgryte@gmail.com>
Date: Fri, 28 Jul 2023 22:11:03 -0600
Subject: [PATCH 1/4] feat: add `array/base/flatten4d-by`

---
 .../@stdlib/array/base/flatten4d-by/README.md | 197 ++++++++
 .../base/flatten4d-by/benchmark/benchmark.js  | 143 ++++++
 .../array/base/flatten4d-by/docs/repl.txt     | 100 +++++
 .../base/flatten4d-by/docs/types/index.d.ts   | 195 ++++++++
 .../base/flatten4d-by/docs/types/test.ts      | 340 ++++++++++++++
 .../array/base/flatten4d-by/examples/index.js |  69 +++
 .../array/base/flatten4d-by/lib/assign.js     | 120 +++++
 .../array/base/flatten4d-by/lib/index.js      |  82 ++++
 .../array/base/flatten4d-by/lib/main.js       | 113 +++++
 .../array/base/flatten4d-by/package.json      |  70 +++
 .../base/flatten4d-by/test/test.assign.js     | 423 ++++++++++++++++++
 .../array/base/flatten4d-by/test/test.js      |  40 ++
 .../array/base/flatten4d-by/test/test.main.js | 250 +++++++++++
 13 files changed, 2142 insertions(+)
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/README.md
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/benchmark/benchmark.js
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/docs/repl.txt
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/docs/types/index.d.ts
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/docs/types/test.ts
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/examples/index.js
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/lib/assign.js
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/lib/index.js
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/lib/main.js
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/package.json
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.assign.js
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.js
 create mode 100644 lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.main.js

diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/README.md b/lib/node_modules/@stdlib/array/base/flatten4d-by/README.md
new file mode 100644
index 00000000000..6aa2e2e7acb
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/README.md
@@ -0,0 +1,197 @@
+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2023 The Stdlib Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+<!-- lint disable maximum-heading-length -->
+
+# flatten4dBy
+
+> Flatten a four-dimensional nested array according to a callback function.
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var flatten4dBy = require( '@stdlib/array/base/flatten4d-by' );
+```
+
+#### flatten4dBy( x, shape, colexicographic, clbk\[, thisArg] )
+
+Flattens a four-dimensional nested array according to a callback function.
+
+```javascript
+function scale( v ) {
+    return v * 2;
+}
+
+var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+var out = flatten4dBy( x, [ 2, 1, 1, 2 ], false, scale );
+// returns [ 2, 4, 6, 8 ]
+```
+
+To flatten in colexicographic order, provide a third argument equal to `true`.
+
+```javascript
+function scale( v ) {
+    return v * 2;
+}
+
+var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+var out = flatten4dBy( x, [ 2, 1, 1, 2 ], true, scale );
+// returns [ 2, 6, 4, 8 ]
+```
+
+To set the callback execution context, provide a `thisArg` argument.
+
+<!-- eslint-disable no-invalid-this -->
+
+```javascript
+function scale( v ) {
+    this.count += 1;
+    return v * 2;
+}
+
+var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+var ctx = {
+    'count': 0
+};
+
+var out = flatten4dBy( x, [ 2, 1, 1, 2 ], false, scale, ctx );
+// returns [ 2, 4, 6, 8 ]
+
+var count = ctx.count;
+// returns 4
+```
+
+#### flatten4dBy.assign( x, shape, colexicographic, out, stride, offset, clbk\[, thisArg] )
+
+Flattens a four-dimensional nested array according to a callback function and assigns elements to a provided output array.
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+function scale( v ) {
+    return v * 2;
+}
+
+var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+var out = new Float64Array( 4 );
+
+var y = flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0 );
+// returns <Float64Array>[ 2, 4, 6, 8 ]
+
+var bool = ( y === out );
+// returns true
+
+y = flatten4dBy.assign( x, [ 2, 1, 1, 2 ], true, out, 1, 0 );
+// returns <Float64Array>[ 2, 6, 4, 8 ]
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   A callback function is provided the following arguments:
+
+    -   **value**: nested array element.
+    -   **indices**: element indices (in lexicographic order).
+    -   **arr**: the input array.
+
+-   Both functions assume that all nested arrays have the same length (i.e., the input array is **not** a ragged array).
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var naryFunction = require( '@stdlib/utils/nary-function' );
+var abs = require( '@stdlib/math/base/special/abs' );
+var flatten4dBy = require( '@stdlib/array/base/flatten4d-by' );
+
+var fcn = naryFunction( abs, 1 );
+
+// Define a 2x2x2x2 array:
+var x = [
+    [
+        [ [ -1, -2 ], [ -3, -4 ] ],
+        [ [ -5, -6 ], [ -7, -8 ] ]
+    ],
+    [
+        [ [ -9, -10 ], [ -11, -12 ] ],
+        [ [ -13, -14 ], [ -15, -16 ] ]
+    ]
+];
+
+var out = flatten4dBy( x, [ 0, 0, 0, 0 ], false, fcn );
+// returns []
+
+out = flatten4dBy( x, [ 0, 0, 0, 0 ], true, fcn );
+// returns []
+
+out = flatten4dBy( x, [ 1, 1, 1, 1 ], false, fcn );
+// returns [ 1 ]
+
+out = flatten4dBy( x, [ 1, 1, 1, 1 ], true, fcn );
+// returns [ 1 ]
+
+out = flatten4dBy( x, [ 1, 2, 2, 2 ], false, fcn );
+// returns [ 1, 2, 3, 4, 5, 6, 7, 8 ]
+
+out = flatten4dBy( x, [ 1, 2, 2, 2 ], true, fcn );
+// returns [ 1, 5, 3, 7, 2, 6, 4, 8 ]
+
+out = flatten4dBy( x, [ 2, 2, 2, 2 ], false, fcn );
+// returns [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ]
+
+out = flatten4dBy( x, [ 2, 2, 2, 2 ], true, fcn );
+// returns [ 1, 9, 5, 13, 3, 11, 7, 15, 2, 10, 6, 14, 4, 12, 8, 16 ]
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+</section>
+
+<!-- /.links -->
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/benchmark/benchmark.js b/lib/node_modules/@stdlib/array/base/flatten4d-by/benchmark/benchmark.js
new file mode 100644
index 00000000000..6243415ea3a
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/benchmark/benchmark.js
@@ -0,0 +1,143 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var isArray = require( '@stdlib/assert/is-array' );
+var isFloat64Array = require( '@stdlib/assert/is-float64array' );
+var zeroTo = require( '@stdlib/array/base/zero-to' );
+var filled = require( '@stdlib/array/base/filled' );
+var Float64Array = require( '@stdlib/array/float64' );
+var pkg = require( './../package.json' ).name;
+var flatten4dBy = require( './../lib' );
+
+
+// FUNCTIONS //
+
+/**
+* Scales an input value.
+*
+* @private
+* @param {number} v - input value
+* @returns {number} output value
+*
+* @example
+* var v = scale( 2.0 );
+* // returns 4.0
+*/
+function scale( v ) {
+	return v * 2.0;
+}
+
+
+// MAIN //
+
+bench( pkg+':size=144,lexicographic', function benchmark( b ) {
+	var x;
+	var i;
+	var v;
+
+	x = filled( filled( filled( zeroTo( 3 ), 4 ), 3 ), 4 );
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		v = flatten4dBy( x, [ 4, 3, 4, 3 ], false, scale );
+		if ( typeof v !== 'object' ) {
+			b.fail( 'should return an array' );
+		}
+	}
+	b.toc();
+	if ( !isArray( v ) ) {
+		b.fail( 'should return an array' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( pkg+':size=144,colexicographic', function benchmark( b ) {
+	var x;
+	var i;
+	var v;
+
+	x = filled( filled( filled( zeroTo( 3 ), 4 ), 3 ), 4 );
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		v = flatten4dBy( x, [ 4, 3, 4, 3 ], true, scale );
+		if ( typeof v !== 'object' ) {
+			b.fail( 'should return an array' );
+		}
+	}
+	b.toc();
+	if ( !isArray( v ) ) {
+		b.fail( 'should return an array' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( pkg+':assign:size=144,lexicographic', function benchmark( b ) {
+	var out;
+	var x;
+	var i;
+	var v;
+
+	out = new Float64Array( 144 );
+	x = filled( filled( filled( zeroTo( 3 ), 4 ), 3 ), 4 );
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		v = flatten4dBy.assign( x, [ 4, 3, 4, 3 ], false, out, 1, 0, scale );
+		if ( typeof v !== 'object' ) {
+			b.fail( 'should return a Float64Array' );
+		}
+	}
+	b.toc();
+	if ( !isFloat64Array( v ) ) {
+		b.fail( 'should return a Float64Array' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( pkg+':assign:size=144,colexicographic', function benchmark( b ) {
+	var out;
+	var x;
+	var i;
+	var v;
+
+	out = new Float64Array( 144 );
+	x = filled( filled( filled( zeroTo( 3 ), 4 ), 3 ), 4 );
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		v = flatten4dBy.assign( x, [ 4, 3, 4, 3 ], true, out, 1, 0, scale );
+		if ( typeof v !== 'object' ) {
+			b.fail( 'should return a Float64Array' );
+		}
+	}
+	b.toc();
+	if ( !isFloat64Array( v ) ) {
+		b.fail( 'should return a Float64Array' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/repl.txt b/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/repl.txt
new file mode 100644
index 00000000000..18ce60bf3d2
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/repl.txt
@@ -0,0 +1,100 @@
+
+{{alias}}( x, shape, colex, clbk[, thisArg] )
+    Flattens a four-dimensional nested array according to a callback function.
+
+    The function assumes that all nested arrays have the same length (i.e., the
+    input array is *not* a ragged array).
+
+    Parameters
+    ----------
+    x: ArrayLikeObject
+        Input array.
+
+    shape: Array<integer>
+        Array shape.
+
+    colex: boolean
+        Specifies whether to flatten array values in colexicographic order.
+
+    clbk: Function
+        Callback function.
+
+    thisArg: any (optional)
+        Callback execution context.
+
+    Returns
+    -------
+    out: Array
+        Flattened array.
+
+    Examples
+    --------
+    > function fcn( v ) { return v * 2; };
+    > var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+    > var out = {{alias}}( x, [ 2, 1, 1, 2 ], false, fcn )
+    [ 2, 4, 6, 8 ]
+    > out = {{alias}}( x, [ 2, 1, 1, 2 ], true, fcn )
+    [ 2, 6, 4, 8 ]
+
+
+{{alias}}.assign( x, shape, colex, out, stride, offset, clbk[, thisArg] )
+    Flattens a four-dimensional nested array according to a callback function
+    and assigns elements to a provided output array.
+
+    The function assumes that all nested arrays have the same length (i.e., the
+    input array is *not* a ragged array).
+
+    The callback function is provided the following arguments:
+
+    - value: nested array element.
+    - indices: element indices (in lexicographic order).
+    - arr: the input array.
+
+    Parameters
+    ----------
+    x: Array
+        Input array.
+
+    shape: Array<integer>
+        Array shape.
+
+    colex: boolean
+        Specifies whether to flatten array values in colexicographic order.
+
+    out: Collection
+        Output array.
+
+    stride: integer
+        Output array stride.
+
+    offset: integer
+        Output array index offset.
+
+    clbk: Function
+        Callback function.
+
+    thisArg: any (optional)
+        Callback execution context.
+
+    Returns
+    -------
+    out: Array
+        Output array.
+
+    Examples
+    --------
+    > function fcn( v ) { return v * 2; };
+    > var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+    > var out = [ 0, 0, 0, 0 ];
+    > var v = {{alias}}.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, fcn )
+    [ 2, 4, 6, 8 ]
+    > var bool = ( v === out )
+    true
+    > out = [ 0, 0, 0, 0 ];
+    > {{alias}}.assign( x, [ 2, 1, 1, 2 ], true, out, 1, 0, fcn );
+    > out
+    [ 2, 6, 4, 8 ]
+
+    See Also
+    --------
+
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/types/index.d.ts b/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/types/index.d.ts
new file mode 100644
index 00000000000..2950453f392
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/types/index.d.ts
@@ -0,0 +1,195 @@
+/*
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+// TypeScript Version: 4.1
+
+/// <reference types="@stdlib/types"/>
+
+import { Collection } from '@stdlib/types/object';
+
+/**
+* Four-dimensional nested array.
+*/
+type Array4D<T> = Array<Array<Array<Collection<T>>>>;
+
+/**
+* Nullary callback function.
+*
+* @returns result
+*/
+type Nullary<U> = () => U;
+
+/**
+* Unary callback function.
+*
+* @param value - array element
+* @returns result
+*/
+type Unary<T, U> = ( value: T ) => U;
+
+/**
+* Binary callback function.
+*
+* @param value - array element
+* @param indices - element indices
+* @returns result
+*/
+type Binary<T, U> = ( value: T, indices: Array<number> ) => U;
+
+/**
+* Ternary callback function.
+*
+* @param value - array element
+* @param indices - element indices
+* @param arr - input array
+* @returns result
+*/
+type Ternary<T, U> = ( value: T, indices: Array<number>, arr: Array4D<T> ) => U;
+
+/**
+* Callback function.
+*
+* @param value - array element
+* @param indices - element indices
+* @param arr - input array
+* @returns result
+*/
+type Callback<T, U> = Nullary<U> | Unary<T, U> | Binary<T, U> | Ternary<T, U>;
+
+/**
+* Interface describing `flatten4dBy`.
+*/
+interface Flatten4dBy {
+	/**
+	* Flattens a four-dimensional nested array according to a callback function.
+	*
+	* ## Notes
+	*
+	* -   The function assumes that all nested arrays have the same length (i.e., the input array is **not** a ragged array).
+	*
+	* @param x - input array
+	* @param shape - array shape
+	* @param colexicographic - specifies whether to flatten array values in colexicographic order
+	* @param clbk - callback function
+	* @param thisArg - callback execution context
+	* @returns flattened array
+	*
+	* @example
+	* function scale( v ) {
+	*     return v * 2;
+	* }
+	*
+	* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	*
+	* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], false, scale );
+	* // returns [ 2, 4, 6, 8 ]
+	*
+	* @example
+	* function scale( v ) {
+	*     return v * 2;
+	* }
+	*
+	* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	*
+	* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], true, scale );
+	* // returns [ 2, 6, 4, 8 ]
+	*/
+	<T = unknown, U = unknown>( x: Array4D<T>, shape: Collection<number>, colexicographic: boolean, clbk: Callback<T, U>, thisArg?: ThisParameterType<Callback<T, U>> ): Array<U>;
+
+	/**
+	* Flattens a four-dimensional nested array according to a callback function and assigns elements to a provided output array.
+	*
+	* ## Notes
+	*
+	* -   The function assumes that all nested arrays have the same length (i.e., the input array is **not** a ragged array).
+	*
+	* @param x - input array
+	* @param shape - array shape
+	* @param colexicographic - specifies whether to flatten array values in colexicographic order
+	* @param out - output array
+	* @param stride - output array stride
+	* @param offset - output array index offset
+	* @param clbk - callback function
+	* @param thisArg - callback execution context
+	* @returns output array
+	*
+	* @example
+	* var Float64Array = require( `@stdlib/array/float64` );
+	*
+	* function scale( v ) {
+	*     return v * 2;
+	* }
+	*
+	* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	*
+	* var out = flatten4dBy.assign( x, [ 2, 2 ], false, new Float64Array( 4 ), 1, 0, scale );
+	* // returns <Float64Array>[ 2, 4, 6, 8 ]
+	*
+	* @example
+	* var Float64Array = require( `@stdlib/array/float64` );
+	*
+	* function scale( v ) {
+	*     return v * 2;
+	* }
+	*
+	* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	*
+	* var out = flatten4dBy.assign( x, [ 2, 2 ], true, new Float64Array( 4 ), 1, 0, scale );
+	* // returns <Float64Array>[ 2, 6, 4, 8 ]
+	*/
+	assign<T = unknown, U = unknown, V = unknown>( x: Array4D<T>, shape: Collection<number>, colexicographic: boolean, out: Collection<V>, stride: number, offset: number, clbk: Callback<T, U>, thisArg?: ThisParameterType<Callback<T, U>> ): Collection<U | V>;
+}
+
+/**
+* Flattens a four-dimensional nested array according to a callback function.
+*
+* ## Notes
+*
+* -   The function assumes that all nested arrays have the same length (i.e., the input array is **not** a ragged array).
+*
+* @param x - input array
+* @param shape - array shape
+* @param colexicographic - specifies whether to flatten array values in colexicographic order
+* @returns flattened array
+*
+* @example
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], false, scale );
+* // returns [ 2, 4, 6, 8 ]
+*
+* @example
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], true, scale );
+* // returns [ 2, 6, 4, 8 ]
+*/
+declare var flatten4dBy: Flatten4dBy;
+
+
+// EXPORTS //
+
+export = flatten4dBy;
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/types/test.ts b/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/types/test.ts
new file mode 100644
index 00000000000..81a42dc7a5e
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+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/docs/types/test.ts
@@ -0,0 +1,340 @@
+/*
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+import flatten4dBy = require( './index' );
+
+/**
+* Identity function.
+*
+* @param v - input value
+* @returns input value
+*/
+function identity<T>( value: T ): T {
+	return value;
+}
+
+
+// TESTS //
+
+// The function returns an array...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+	flatten4dBy<number, number>( x, [ 2, 1, 1, 2 ], false, identity ); // $ExpectType number[]
+	flatten4dBy<number, number>( x, [ 2, 1, 1, 2 ], true, identity ); // $ExpectType number[]
+
+	flatten4dBy<number, number>( x, [ 2, 1, 1, 2 ], false, identity, {} ); // $ExpectType number[]
+	flatten4dBy<number, number>( x, [ 2, 1, 1, 2 ], true, identity, {} ); // $ExpectType number[]
+
+	flatten4dBy<string, string>( [ [ [ [ '1', '2' ] ] ], [ [ [ '3', '4' ] ] ] ], [ 2, 1, 1, 2 ], false, identity ); // $ExpectType string[]
+	flatten4dBy<string, string>( [ [ [ [ '1', '2' ] ] ], [ [ [ '3', '4' ] ] ] ], [ 2, 1, 1, 2 ], true, identity ); // $ExpectType string[]
+
+	flatten4dBy<string, string>( [ [ [ [ '1', '2' ] ] ], [ [ [ '3', '4' ] ] ] ], [ 2, 1, 1, 2 ], false, identity, {} ); // $ExpectType string[]
+	flatten4dBy<string, string>( [ [ [ [ '1', '2' ] ] ], [ [ [ '3', '4' ] ] ] ], [ 2, 1, 1, 2 ], true, identity, {} ); // $ExpectType string[]
+}
+
+// The compiler throws an error if the function is provided a first argument which is not an array-like object...
+{
+	flatten4dBy( 1, [ 2, 1, 1, 2 ], false, identity ); // $ExpectError
+	flatten4dBy( true, [ 2, 1, 1, 2 ], false, identity ); // $ExpectError
+	flatten4dBy( false, [ 2, 1, 1, 2 ], false, identity ); // $ExpectError
+	flatten4dBy( null, [ 2, 1, 1, 2 ], false, identity ); // $ExpectError
+	flatten4dBy( void 0, [ 2, 1, 1, 2 ], false, identity ); // $ExpectError
+	flatten4dBy( {}, [ 2, 1, 1, 2 ], false, identity ); // $ExpectError
+
+	flatten4dBy( 1, [ 2, 1, 1, 2 ], false, identity, {} ); // $ExpectError
+	flatten4dBy( true, [ 2, 1, 1, 2 ], false, identity, {} ); // $ExpectError
+	flatten4dBy( false, [ 2, 1, 1, 2 ], false, identity, {} ); // $ExpectError
+	flatten4dBy( null, [ 2, 1, 1, 2 ], false, identity, {} ); // $ExpectError
+	flatten4dBy( void 0, [ 2, 1, 1, 2 ], false, identity, {} ); // $ExpectError
+	flatten4dBy( {}, [ 2, 1, 1, 2 ], false, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the function is provided a second argument which is not an array-like object containing numbers...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+	flatten4dBy( x, '', false, identity ); // $ExpectError
+	flatten4dBy( x, 1, false, identity ); // $ExpectError
+	flatten4dBy( x, true, false, identity ); // $ExpectError
+	flatten4dBy( x, false, false, identity ); // $ExpectError
+	flatten4dBy( x, null, false, identity ); // $ExpectError
+	flatten4dBy( x, void 0, false, identity ); // $ExpectError
+	flatten4dBy( x, {}, false, identity ); // $ExpectError
+	flatten4dBy( x, [ 1, '2', 3 ], false, identity ); // $ExpectError
+	flatten4dBy( x, ( x: number ): number => x, false, identity ); // $ExpectError
+
+	flatten4dBy( x, '', false, identity, {} ); // $ExpectError
+	flatten4dBy( x, 1, false, identity, {} ); // $ExpectError
+	flatten4dBy( x, true, false, identity, {} ); // $ExpectError
+	flatten4dBy( x, false, false, identity, {} ); // $ExpectError
+	flatten4dBy( x, null, false, identity, {} ); // $ExpectError
+	flatten4dBy( x, void 0, false, identity, {} ); // $ExpectError
+	flatten4dBy( x, {}, false, identity, {} ); // $ExpectError
+	flatten4dBy( x, [ 1, '2', 3 ], false, identity, {} ); // $ExpectError
+	flatten4dBy( x, ( x: number ): number => x, false, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the function is provided a third argument which is not a boolean...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+	flatten4dBy( x, [ 2, 1, 1, 2 ], '', identity ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], 1, identity ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], null, identity ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], void 0, identity ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], {}, identity ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], [], identity ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], ( x: number ): number => x, identity ); // $ExpectError
+
+	flatten4dBy( x, [ 2, 1, 1, 2 ], '', identity, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], 1, identity, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], null, identity, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], void 0, identity, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], {}, identity, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], [], identity, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], ( x: number ): number => x, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the function is provided a fourth argument which is not a function...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, '' ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, 1 ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, true ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, false ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, null ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, void 0 ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, [] ); // $ExpectError
+
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, '', {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, 1, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, true, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, false, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, null, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, void 0, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, {}, {} ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, [], {} ); // $ExpectError
+}
+
+// The compiler throws an error if the function is provided an unsupported number of arguments...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+	flatten4dBy(); // $ExpectError
+	flatten4dBy( x ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ] ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false ); // $ExpectError
+	flatten4dBy( x, [ 2, 1, 1, 2 ], false, identity, {}, {} ); // $ExpectError
+}
+
+// Attached to the main export is an `assign` method which returns a collection...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+	const out1 = [ 0, 0, 0, 0 ];
+
+	flatten4dBy.assign<number, number, number>( x, [ 2, 1, 1, 2 ], false, out1, 1, 0, identity ); // $ExpectType Collection<number>
+	flatten4dBy.assign<number, number, number>( x, [ 2, 1, 1, 2 ], true, out1, 1, 0, identity ); // $ExpectType Collection<number>
+
+	flatten4dBy.assign<number, number, number>( x, [ 2, 1, 1, 2 ], false, out1, 1, 0, identity, {} ); // $ExpectType Collection<number>
+	flatten4dBy.assign<number, number, number>( x, [ 2, 1, 1, 2 ], true, out1, 1, 0, identity, {} ); // $ExpectType Collection<number>
+
+	const out2 = [ '', '', '', '' ];
+
+	flatten4dBy.assign<string, string, string>( [ [ [ [ '1', '2' ] ] ], [ [ [ '3', '4' ] ] ] ], [ 2, 1, 1, 2 ], false, out2, 1, 0, identity ); // $ExpectType Collection<string>
+	flatten4dBy.assign<string, string, string>( [ [ [ [ '1', '2' ] ] ], [ [ [ '3', '4' ] ] ] ], [ 2, 1, 1, 2 ], true, out2, 1, 0, identity ); // $ExpectType Collection<string>
+
+	flatten4dBy.assign<string, string, string>( [ [ [ [ '1', '2' ] ] ], [ [ [ '3', '4' ] ] ] ], [ 2, 1, 1, 2 ], false, out2, 1, 0, identity, {} ); // $ExpectType Collection<string>
+	flatten4dBy.assign<string, string, string>( [ [ [ [ '1', '2' ] ] ], [ [ [ '3', '4' ] ] ] ], [ 2, 1, 1, 2 ], true, out2, 1, 0, identity, {} ); // $ExpectType Collection<string>
+}
+
+// The compiler throws an error if the `assign` method is provided a first argument which is not an array-like object...
+{
+	const out = [ 0, 0, 0, 0 ];
+
+	flatten4dBy.assign( 1, [ 2, 1, 1, 2 ], false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( true, [ 2, 1, 1, 2 ], false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( false, [ 2, 1, 1, 2 ], false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( null, [ 2, 1, 1, 2 ], false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( void 0, [ 2, 1, 1, 2 ], false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( {}, [ 2, 1, 1, 2 ], false, out, 1, 0, identity ); // $ExpectError
+
+	flatten4dBy.assign( 1, [ 2, 1, 1, 2 ], false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( true, [ 2, 1, 1, 2 ], false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( false, [ 2, 1, 1, 2 ], false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( null, [ 2, 1, 1, 2 ], false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( void 0, [ 2, 1, 1, 2 ], false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( {}, [ 2, 1, 1, 2 ], false, out, 1, 0, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the `assign` method is provided a second argument which is not an array-like object containing numbers...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	const out = [ 0, 0, 0, 0 ];
+
+	flatten4dBy.assign( x, '', false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, 1, false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, true, false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, false, false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, null, false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, void 0, false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, {}, false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 1, '2', 3 ], false, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, ( x: number ): number => x, false, out, 1, 0, identity ); // $ExpectError
+
+	flatten4dBy.assign( x, '', false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, 1, false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, true, false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, false, false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, null, false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, void 0, false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, {}, false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 1, '2', 3 ], false, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, ( x: number ): number => x, false, out, 1, 0, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the `assign` method is provided a third argument which is not a boolean...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	const out = [ 0, 0, 0, 0 ];
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], '', out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], 1, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], null, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], void 0, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], {}, out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], [], out, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], ( x: number ): number => x, out, 1, 0, identity ); // $ExpectError
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], '', out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], 1, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], null, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], void 0, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], {}, out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], [], out, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], ( x: number ): number => x, out, 1, 0, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the `assign` method is provided a fourth argument which is not an array-like object...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, 1, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, true, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, false, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, null, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, void 0, 1, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, {}, 1, 0, identity ); // $ExpectError
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, 1, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, true, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, false, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, null, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, void 0, 1, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, {}, 1, 0, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the `assign` method is provided a fifth argument which is not a number...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	const out = [ 0, 0, 0, 0 ];
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, '1', 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, true, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, false, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, null, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, void 0, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, {}, 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, [], 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, ( x: number ): number => x, 0, identity ); // $ExpectError
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, '1', 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, true, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, false, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, null, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, void 0, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, {}, 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, [], 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, ( x: number ): number => x, 0, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the `assign` method is provided a sixth argument which is not a number...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	const out = [ 0, 0, 0, 0 ];
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, '1', identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, true, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, false, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, null, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, void 0, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, {}, identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, [], identity ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, ( x: number ): number => x, identity ); // $ExpectError
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, '1', identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, true, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, false, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, null, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, void 0, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, {}, identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, [], identity, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, ( x: number ): number => x, identity, {} ); // $ExpectError
+}
+
+// The compiler throws an error if the `assign` method is provided a seventh argument which is not a function...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	const out = [ 0, 0, 0, 0 ];
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, '1' ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, 1 ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, true ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, false ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, null ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, void 0 ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, [] ); // $ExpectError
+
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, '1', {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, 1, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, true, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, false, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, null, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, void 0, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, {}, {} ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, [], {} ); // $ExpectError
+}
+
+// The compiler throws an error if the `assign` method is provided an unsupported number of arguments...
+{
+	const x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+	const out = [ 0, 0, 0, 0 ];
+
+	flatten4dBy.assign(); // $ExpectError
+	flatten4dBy.assign( x ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ] ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1 ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0 ); // $ExpectError
+	flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, identity, {}, {} ); // $ExpectError
+}
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/examples/index.js b/lib/node_modules/@stdlib/array/base/flatten4d-by/examples/index.js
new file mode 100644
index 00000000000..eb5f6a3417b
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/examples/index.js
@@ -0,0 +1,69 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+var naryFunction = require( '@stdlib/utils/nary-function' );
+var abs = require( '@stdlib/math/base/special/abs' );
+var flatten4dBy = require( './../lib' );
+
+var fcn = naryFunction( abs, 1 );
+
+// Define a 2x2x2x2 array:
+var x = [
+	[
+		[ [ -1, -2 ], [ -3, -4 ] ],
+		[ [ -5, -6 ], [ -7, -8 ] ]
+	],
+	[
+		[ [ -9, -10 ], [ -11, -12 ] ],
+		[ [ -13, -14 ], [ -15, -16 ] ]
+	]
+];
+
+var out = flatten4dBy( x, [ 0, 0, 0, 0 ], false, fcn );
+console.log( out );
+// => []
+
+out = flatten4dBy( x, [ 0, 0, 0, 0 ], true, fcn );
+console.log( out );
+// => []
+
+out = flatten4dBy( x, [ 1, 1, 1, 1 ], false, fcn );
+console.log( out );
+// => [ 1 ]
+
+out = flatten4dBy( x, [ 1, 1, 1, 1 ], true, fcn );
+console.log( out );
+// => [ 1 ]
+
+out = flatten4dBy( x, [ 1, 2, 2, 2 ], false, fcn );
+console.log( out );
+// => [ 1, 2, 3, 4, 5, 6, 7, 8 ]
+
+out = flatten4dBy( x, [ 1, 2, 2, 2 ], true, fcn );
+console.log( out );
+// => [ 1, 5, 3, 7, 2, 6, 4, 8 ]
+
+out = flatten4dBy( x, [ 2, 2, 2, 2 ], false, fcn );
+console.log( out );
+// => [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ]
+
+out = flatten4dBy( x, [ 2, 2, 2, 2 ], true, fcn );
+console.log( out );
+// => [ 1, 9, 5, 13, 3, 11, 7, 15, 2, 10, 6, 14, 4, 12, 8, 16 ]
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/assign.js b/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/assign.js
new file mode 100644
index 00000000000..2e546441540
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/assign.js
@@ -0,0 +1,120 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+/* eslint-disable max-len */
+
+'use strict';
+
+// MAIN //
+
+/**
+* Flattens a four-dimensional nested array according to a callback function and assigns elements to a provided output array.
+*
+* ## Notes
+*
+* -   The function assumes that all nested arrays have the same length (i.e., the input array is **not** a ragged array).
+*
+* @param {Array<Array<Collection>>} x - input nested array
+* @param {NonNegativeIntegerArray} shape - array shape
+* @param {boolean} colexicographic - specifies whether to flatten array values in colexicographic order
+* @param {Collection} out - output array
+* @param {integer} stride - output array stride
+* @param {NonNegativeInteger} offset - output array index offset
+* @param {Function} clbk - callback function
+* @param {*} [thisArg] - callback execution context
+* @returns {Collection} output array
+*
+* @example
+* var Float64Array = require( '@stdlib/array/float64' );
+*
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], false, new Float64Array( 4 ), 1, 0, scale );
+* // returns <Float64Array>[ 2, 4, 6, 8 ]
+*
+* @example
+* var Float64Array = require( '@stdlib/array/float64' );
+*
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], true, new Float64Array( 4 ), 1, 0, scale );
+* // returns <Float64Array>[ 2, 6, 4, 8 ]
+*/
+function flatten4dBy( x, shape, colexicographic, out, stride, offset, clbk, thisArg ) {
+	var S0;
+	var S1;
+	var S2;
+	var S3;
+	var i0;
+	var i1;
+	var i2;
+	var i3;
+	var a0;
+	var a1;
+	var a2;
+	var io;
+
+	// Extract loop variables:
+	S0 = shape[ 3 ]; // for nested arrays, the last dimensions have the fastest changing indices
+	S1 = shape[ 2 ];
+	S2 = shape[ 1 ];
+	S3 = shape[ 0 ];
+
+	// Iterate over the array dimensions...
+	io = offset;
+	if ( colexicographic ) {
+		for ( i0 = 0; i0 < S0; i0++ ) {
+			for ( i1 = 0; i1 < S1; i1++ ) {
+				for ( i2 = 0; i2 < S2; i2++ ) {
+					for ( i3 = 0; i3 < S3; i3++ ) {
+						out[ io ] = clbk.call( thisArg, x[ i3 ][ i2 ][ i1 ][ i0 ], [ i3, i2, i1, i0 ], x ); // equivalent to storing in column-major (Fortran-style) order
+						io += stride;
+					}
+				}
+			}
+		}
+		return out;
+	}
+	for ( i3 = 0; i3 < S3; i3++ ) {
+		a2 = x[ i3 ];
+		for ( i2 = 0; i2 < S2; i2++ ) {
+			a1 = a2[ i2 ];
+			for ( i1 = 0; i1 < S1; i1++ ) {
+				a0 = a1[ i1 ];
+				for ( i0 = 0; i0 < S0; i0++ ) {
+					out[ io ] = clbk.call( thisArg, a0[ i0 ], [ i3, i2, i1, i0 ], x ); // equivalent to storing in row-major (C-style) order
+					io += stride;
+				}
+			}
+		}
+	}
+	return out;
+}
+
+
+// EXPORTS //
+
+module.exports = flatten4dBy;
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/index.js b/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/index.js
new file mode 100644
index 00000000000..1a8648cdec3
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/index.js
@@ -0,0 +1,82 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+/**
+* Flatten a four-dimensional nested array according to a callback function.
+*
+* @module @stdlib/array/base/flatten4d-by
+*
+* @example
+* var flatten4dBy = require( '@stdlib/array/base/flatten4d-by' );
+*
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], false, scale );
+* // returns [ 2, 4, 6, 8 ]
+*
+* @example
+* var flatten4dBy = require( '@stdlib/array/base/flatten4d-by' );
+*
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], true, scale );
+* // returns [ 2, 6, 4, 8 ]
+*
+* @example
+* var Float64Array = require( '@stdlib/array/float64' );
+* var flatten4dBy = require( '@stdlib/array/base/flatten4d-by' );
+*
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = new Float64Array( 4 );
+* var y = flatten4dBy.assign( x, [ 2, 1, 1, 2 ], true, out, 1, 0, scale );
+* // returns <Float64Array>[ 2, 6, 4, 8 ]
+*
+* var bool = ( y === out );
+* // returns true
+*/
+
+// MODULES //
+
+var setReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
+var main = require( './main.js' );
+var assign = require( './assign.js' );
+
+
+// MAIN //
+
+setReadOnly( main, 'assign', assign );
+
+
+// EXPORTS //
+
+module.exports = main;
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/main.js b/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/main.js
new file mode 100644
index 00000000000..534bfa127af
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/lib/main.js
@@ -0,0 +1,113 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+/* eslint-disable max-len */
+
+'use strict';
+
+// MAIN //
+
+/**
+* Flattens a four-dimensional nested array according to a callback function.
+*
+* ## Notes
+*
+* -   The function assumes that all nested arrays have the same length (i.e., the input array is **not** a ragged array).
+*
+* @param {Array<Array<Collection>>} x - input nested array
+* @param {NonNegativeIntegerArray} shape - array shape
+* @param {boolean} colexicographic - specifies whether to flatten array values in colexicographic order
+* @param {Function} clbk - callback function
+* @param {*} [thisArg] - callback execution context
+* @returns {Array} flattened array
+*
+* @example
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], false, scale );
+* // returns [ 2, 4, 6, 8 ]
+*
+* @example
+* function scale( v ) {
+*     return v * 2;
+* }
+*
+* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
+*
+* var out = flatten4dBy( x, [ 2, 1, 1, 2 ], true, scale );
+* // returns [ 2, 6, 4, 8 ]
+*/
+function flatten4dBy( x, shape, colexicographic, clbk, thisArg ) {
+	var out;
+	var S0;
+	var S1;
+	var S2;
+	var S3;
+	var i0;
+	var i1;
+	var i2;
+	var i3;
+	var a0;
+	var a1;
+	var a2;
+
+	// Extract loop variables:
+	S0 = shape[ 3 ]; // for nested arrays, the last dimensions have the fastest changing indices
+	S1 = shape[ 2 ];
+	S2 = shape[ 1 ];
+	S3 = shape[ 0 ];
+
+	// Initialize an output array:
+	out = [];
+
+	// Iterate over the array dimensions...
+	if ( colexicographic ) {
+		for ( i0 = 0; i0 < S0; i0++ ) {
+			for ( i1 = 0; i1 < S1; i1++ ) {
+				for ( i2 = 0; i2 < S2; i2++ ) {
+					for ( i3 = 0; i3 < S3; i3++ ) {
+						out.push( clbk.call( thisArg, x[ i3 ][ i2 ][ i1 ][ i0 ], [ i3, i2, i1, i0 ], x ) ); // equivalent to storing in column-major (Fortran-style) order
+					}
+				}
+			}
+		}
+		return out;
+	}
+	for ( i3 = 0; i3 < S3; i3++ ) {
+		a2 = x[ i3 ];
+		for ( i2 = 0; i2 < S2; i2++ ) {
+			a1 = a2[ i2 ];
+			for ( i1 = 0; i1 < S1; i1++ ) {
+				a0 = a1[ i1 ];
+				for ( i0 = 0; i0 < S0; i0++ ) {
+					out.push( clbk.call( thisArg, a0[ i0 ], [ i3, i2, i1, i0 ], x ) ); // equivalent to storing in row-major (C-style) order
+				}
+			}
+		}
+	}
+	return out;
+}
+
+
+// EXPORTS //
+
+module.exports = flatten4dBy;
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/package.json b/lib/node_modules/@stdlib/array/base/flatten4d-by/package.json
new file mode 100644
index 00000000000..fc4282ccca8
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/package.json
@@ -0,0 +1,70 @@
+{
+  "name": "@stdlib/array/base/flatten4d-by",
+  "version": "0.0.0",
+  "description": "Flatten a four-dimensional nested array according to a callback function.",
+  "license": "Apache-2.0",
+  "author": {
+    "name": "The Stdlib Authors",
+    "url": "https://github.com/stdlib-js/stdlib/graphs/contributors"
+  },
+  "contributors": [
+    {
+      "name": "The Stdlib Authors",
+      "url": "https://github.com/stdlib-js/stdlib/graphs/contributors"
+    }
+  ],
+  "main": "./lib",
+  "directories": {
+    "benchmark": "./benchmark",
+    "doc": "./docs",
+    "example": "./examples",
+    "lib": "./lib",
+    "test": "./test"
+  },
+  "types": "./docs/types",
+  "scripts": {},
+  "homepage": "https://github.com/stdlib-js/stdlib",
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/stdlib-js/stdlib.git"
+  },
+  "bugs": {
+    "url": "https://github.com/stdlib-js/stdlib/issues"
+  },
+  "dependencies": {},
+  "devDependencies": {},
+  "engines": {
+    "node": ">=0.10.0",
+    "npm": ">2.7.0"
+  },
+  "os": [
+    "aix",
+    "darwin",
+    "freebsd",
+    "linux",
+    "macos",
+    "openbsd",
+    "sunos",
+    "win32",
+    "windows"
+  ],
+  "keywords": [
+    "stdlib",
+    "utilities",
+    "utils",
+    "generic",
+    "array",
+    "flatten",
+    "flat",
+    "4d",
+    "tensor",
+    "strided",
+    "ndarray",
+    "multidimensional",
+    "foreach",
+    "map",
+    "transform",
+    "callback",
+    "accessor"
+  ]
+}
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.assign.js b/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.assign.js
new file mode 100644
index 00000000000..64adc57d3c7
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.assign.js
@@ -0,0 +1,423 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var tape = require( 'tape' );
+var naryFunction = require( '@stdlib/utils/nary-function' );
+var abs = require( '@stdlib/math/base/special/abs' );
+var Float64Array = require( '@stdlib/array/float64' );
+var flatten4dBy = require( './../lib/assign.js' );
+
+
+// VARIABLES //
+
+var clbk = naryFunction( abs, 1 );
+
+
+// TESTS //
+
+tape( 'main export is a function', function test( t ) {
+	t.ok( true, __filename );
+	t.strictEqual( typeof flatten4dBy, 'function', 'main export is a function' );
+	t.end();
+});
+
+tape( 'the function flattens a nested array (lexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			],
+			[
+				[ -5, -6 ],
+				[ -7, -8 ]
+			]
+		],
+		[
+			[
+				[ -9, -10 ],
+				[ -11, -12 ]
+			],
+			[
+				[ -13, -14 ],
+				[ -15, -16 ]
+			]
+		]
+	];
+
+	expected = new Float64Array( [] );
+	out = new Float64Array( 0 );
+	actual = flatten4dBy( x, [ 0, 0, 0, 0 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [] );
+	out = new Float64Array( 0 );
+	actual = flatten4dBy( x, [ 0, 0, 1, 0 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [] );
+	out = new Float64Array( 0 );
+	actual = flatten4dBy( x, [ 1, 0, 0, 1 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1 ] );
+	out = new Float64Array( 1 );
+	actual = flatten4dBy( x, [ 1, 1, 1, 1 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 2 ] );
+	out = new Float64Array( 2 );
+	actual = flatten4dBy( x, [ 1, 1, 1, 2 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 9 ] );
+	out = new Float64Array( 2 );
+	actual = flatten4dBy( x, [ 2, 1, 1, 1 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 2, 5, 6 ] );
+	out = new Float64Array( 4 );
+	actual = flatten4dBy( x, [ 1, 2, 1, 2 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 2, 3, 4, 5, 6, 7, 8 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 1, 2, 2, 2 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 5, 9, 13 ] );
+	out = new Float64Array( 4 );
+	actual = flatten4dBy( x, [ 2, 2, 1, 1 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 2, 5, 6, 9, 10, 13, 14 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 2, 2, 1, 2 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ] ); // eslint-disable-line max-len
+	out = new Float64Array( 16 );
+	actual = flatten4dBy( x, [ 2, 2, 2, 2 ], false, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function flattens a nested array (colexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			],
+			[
+				[ -5, -6 ],
+				[ -7, -8 ]
+			]
+		],
+		[
+			[
+				[ -9, -10 ],
+				[ -11, -12 ]
+			],
+			[
+				[ -13, -14 ],
+				[ -15, -16 ]
+			]
+		]
+	];
+
+	expected = new Float64Array( [] );
+	out = new Float64Array( 0 );
+	actual = flatten4dBy( x, [ 0, 0, 0, 0 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [] );
+	out = new Float64Array( 0 );
+	actual = flatten4dBy( x, [ 0, 0, 1, 0 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [] );
+	out = new Float64Array( 0 );
+	actual = flatten4dBy( x, [ 1, 0, 0, 1 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1 ] );
+	out = new Float64Array( 1 );
+	actual = flatten4dBy( x, [ 1, 1, 1, 1 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 2 ] );
+	out = new Float64Array( 2 );
+	actual = flatten4dBy( x, [ 1, 1, 1, 2 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 9 ] );
+	out = new Float64Array( 2 );
+	actual = flatten4dBy( x, [ 2, 1, 1, 1 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 5, 2, 6 ] );
+	out = new Float64Array( 4 );
+	actual = flatten4dBy( x, [ 1, 2, 1, 2 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 5, 3, 7, 2, 6, 4, 8 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 1, 2, 2, 2 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 9, 5, 13 ] );
+	out = new Float64Array( 4 );
+	actual = flatten4dBy( x, [ 2, 2, 1, 1 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 9, 5, 13, 2, 10, 6, 14 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 2, 2, 1, 2 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = new Float64Array( [ 1, 9, 5, 13, 3, 11, 7, 15, 2, 10, 6, 14, 4, 12, 8, 16 ] ); // eslint-disable-line max-len
+	out = new Float64Array( 16 );
+	actual = flatten4dBy( x, [ 2, 2, 2, 2 ], true, out, 1, 0, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports providing a stride (lexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	expected = new Float64Array( [ 1, 0, 2, 0, 3, 0, 4, 0 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 1, 1, 2, 2 ], false, out, 2, 0, clbk );
+	t.strictEqual( actual, out, 'returns expected value' );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports providing a stride (colexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	expected = new Float64Array( [ 1, 0, 3, 0, 2, 0, 4, 0 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 1, 1, 2, 2 ], true, out, 2, 0, clbk );
+	t.strictEqual( actual, out, 'returns expected value' );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports providing an offset (lexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	expected = new Float64Array( [ 0, 0, 1, 2, 3, 4, 0, 0 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 1, 1, 2, 2 ], false, out, 1, 2, clbk );
+	t.strictEqual( actual, out, 'returns expected value' );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports providing an offset (colexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	expected = new Float64Array( [ 0, 0, 1, 3, 2, 4, 0, 0 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 1, 1, 2, 2 ], true, out, 1, 2, clbk );
+	t.strictEqual( actual, out, 'returns expected value' );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports complex access patterns (lexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	expected = new Float64Array( [ 0, 4, 0, 3, 0, 2, 0, 1 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 1, 1, 2, 2 ], false, out, -2, 7, clbk );
+	t.strictEqual( actual, out, 'returns expected value' );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports complex access patterns (colexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	expected = new Float64Array( [ 0, 4, 0, 2, 0, 3, 0, 1 ] );
+	out = new Float64Array( 8 );
+	actual = flatten4dBy( x, [ 1, 1, 2, 2 ], true, out, -2, 7, clbk );
+	t.strictEqual( actual, out, 'returns expected value' );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports setting the callback execution context (lexicographic)', function test( t ) {
+	var ctx;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	ctx = {
+		'count': 0
+	};
+
+	out = new Float64Array( 4 );
+	flatten4dBy( x, [ 1, 1, 2, 2 ], false, out, 1, 0, fcn, ctx );
+	t.strictEqual( ctx.count, 4, 'returns expected value' );
+
+	t.end();
+
+	function fcn( value, indices, arr ) {
+		this.count += 1; // eslint-disable-line no-invalid-this
+		t.strictEqual( indices.length, 4, 'returns expected value' );
+		t.strictEqual( value, arr[ indices[0] ][ indices[1] ][ indices[2] ][ indices[3] ], 'returns expected value' );
+		t.strictEqual( arr, x, 'returns expected value' );
+	}
+});
+
+tape( 'the function supports setting the callback execution context (colexicographic)', function test( t ) {
+	var ctx;
+	var out;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	ctx = {
+		'count': 0
+	};
+
+	out = new Float64Array( 4 );
+	flatten4dBy( x, [ 1, 1, 2, 2 ], true, out, 1, 0, fcn, ctx );
+	t.strictEqual( ctx.count, 4, 'returns expected value' );
+
+	t.end();
+
+	function fcn( value, indices, arr ) {
+		this.count += 1; // eslint-disable-line no-invalid-this
+		t.strictEqual( indices.length, 4, 'returns expected value' );
+		t.strictEqual( value, arr[ indices[0] ][ indices[1] ][ indices[2] ][ indices[3] ], 'returns expected value' );
+		t.strictEqual( arr, x, 'returns expected value' );
+	}
+});
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.js b/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.js
new file mode 100644
index 00000000000..0f7ef980fef
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.js
@@ -0,0 +1,40 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var tape = require( 'tape' );
+var hasOwnProp = require( '@stdlib/assert/has-own-property' );
+var flatten4dBy = require( './../lib' );
+
+
+// TESTS //
+
+tape( 'main export is a function', function test( t ) {
+	t.ok( true, __filename );
+	t.strictEqual( typeof flatten4dBy, 'function', 'main export is a function' );
+	t.end();
+});
+
+tape( 'attached to the main export is an `assign` method', function test( t ) {
+	t.strictEqual( hasOwnProp( flatten4dBy, 'assign' ), true, 'has property' );
+	t.strictEqual( typeof flatten4dBy.assign, 'function', 'has method' );
+	t.end();
+});
diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.main.js b/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.main.js
new file mode 100644
index 00000000000..9172f224d9e
--- /dev/null
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/test/test.main.js
@@ -0,0 +1,250 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var tape = require( 'tape' );
+var naryFunction = require( '@stdlib/utils/nary-function' );
+var abs = require( '@stdlib/math/base/special/abs' );
+var flatten4dBy = require( './../lib/main.js' );
+
+
+// VARIABLES //
+
+var clbk = naryFunction( abs, 1 );
+
+
+// TESTS //
+
+tape( 'main export is a function', function test( t ) {
+	t.ok( true, __filename );
+	t.strictEqual( typeof flatten4dBy, 'function', 'main export is a function' );
+	t.end();
+});
+
+tape( 'the function flattens a nested array (lexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			],
+			[
+				[ -5, -6 ],
+				[ -7, -8 ]
+			]
+		],
+		[
+			[
+				[ -9, -10 ],
+				[ -11, -12 ]
+			],
+			[
+				[ -13, -14 ],
+				[ -15, -16 ]
+			]
+		]
+	];
+
+	expected = [];
+	actual = flatten4dBy( x, [ 0, 0, 0, 0 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [];
+	actual = flatten4dBy( x, [ 0, 0, 1, 0 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [];
+	actual = flatten4dBy( x, [ 1, 0, 0, 1 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1 ];
+	actual = flatten4dBy( x, [ 1, 1, 1, 1 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 2 ];
+	actual = flatten4dBy( x, [ 1, 1, 1, 2 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 9 ];
+	actual = flatten4dBy( x, [ 2, 1, 1, 1 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 2, 5, 6 ];
+	actual = flatten4dBy( x, [ 1, 2, 1, 2 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 2, 3, 4, 5, 6, 7, 8 ];
+	actual = flatten4dBy( x, [ 1, 2, 2, 2 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 5, 9, 13 ];
+	actual = flatten4dBy( x, [ 2, 2, 1, 1 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 2, 5, 6, 9, 10, 13, 14 ];
+	actual = flatten4dBy( x, [ 2, 2, 1, 2 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ];
+	actual = flatten4dBy( x, [ 2, 2, 2, 2 ], false, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function flattens a nested array (colexicographic)', function test( t ) {
+	var expected;
+	var actual;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			],
+			[
+				[ -5, -6 ],
+				[ -7, -8 ]
+			]
+		],
+		[
+			[
+				[ -9, -10 ],
+				[ -11, -12 ]
+			],
+			[
+				[ -13, -14 ],
+				[ -15, -16 ]
+			]
+		]
+	];
+
+	expected = [];
+	actual = flatten4dBy( x, [ 0, 0, 0, 0 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [];
+	actual = flatten4dBy( x, [ 0, 0, 1, 0 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [];
+	actual = flatten4dBy( x, [ 1, 0, 0, 1 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1 ];
+	actual = flatten4dBy( x, [ 1, 1, 1, 1 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 2 ];
+	actual = flatten4dBy( x, [ 1, 1, 1, 2 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 9 ];
+	actual = flatten4dBy( x, [ 2, 1, 1, 1 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 5, 2, 6 ];
+	actual = flatten4dBy( x, [ 1, 2, 1, 2 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 5, 3, 7, 2, 6, 4, 8 ];
+	actual = flatten4dBy( x, [ 1, 2, 2, 2 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 9, 5, 13 ];
+	actual = flatten4dBy( x, [ 2, 2, 1, 1 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 9, 5, 13, 2, 10, 6, 14 ];
+	actual = flatten4dBy( x, [ 2, 2, 1, 2 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	expected = [ 1, 9, 5, 13, 3, 11, 7, 15, 2, 10, 6, 14, 4, 12, 8, 16 ];
+	actual = flatten4dBy( x, [ 2, 2, 2, 2 ], true, clbk );
+	t.deepEqual( actual, expected, 'returns expected value' );
+
+	t.end();
+});
+
+tape( 'the function supports setting the callback execution context (lexicographic)', function test( t ) {
+	var ctx;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	ctx = {
+		'count': 0
+	};
+
+	flatten4dBy( x, [ 1, 1, 2, 2 ], false, fcn, ctx );
+	t.strictEqual( ctx.count, 4, 'returns expected value' );
+
+	t.end();
+
+	function fcn( value, indices, arr ) {
+		this.count += 1; // eslint-disable-line no-invalid-this
+		t.strictEqual( indices.length, 4, 'returns expected value' );
+		t.strictEqual( value, arr[ indices[0] ][ indices[1] ][ indices[2] ][ indices[3] ], 'returns expected value' );
+		t.strictEqual( arr, x, 'returns expected value' );
+	}
+});
+
+tape( 'the function supports setting the callback execution context (colexicographic)', function test( t ) {
+	var ctx;
+	var x;
+
+	x = [
+		[
+			[
+				[ -1, -2 ],
+				[ -3, -4 ]
+			]
+		]
+	];
+
+	ctx = {
+		'count': 0
+	};
+
+	flatten4dBy( x, [ 1, 1, 2, 2 ], true, fcn, ctx );
+	t.strictEqual( ctx.count, 4, 'returns expected value' );
+
+	t.end();
+
+	function fcn( value, indices, arr ) {
+		this.count += 1; // eslint-disable-line no-invalid-this
+		t.strictEqual( indices.length, 4, 'returns expected value' );
+		t.strictEqual( value, arr[ indices[0] ][ indices[1] ][ indices[2] ][ indices[3] ], 'returns expected value' );
+		t.strictEqual( arr, x, 'returns expected value' );
+	}
+});

From 3dbf75f15770e6f3b3bc1b60d9135f969b19a40f Mon Sep 17 00:00:00 2001
From: Athan Reines <kgryte@gmail.com>
Date: Fri, 28 Jul 2023 22:11:39 -0600
Subject: [PATCH 2/4] feat: add `flatten4dBy` to namespace

---
 lib/node_modules/@stdlib/array/base/lib/index.js | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/node_modules/@stdlib/array/base/lib/index.js b/lib/node_modules/@stdlib/array/base/lib/index.js
index e130ae705ba..a44580821d3 100644
--- a/lib/node_modules/@stdlib/array/base/lib/index.js
+++ b/lib/node_modules/@stdlib/array/base/lib/index.js
@@ -207,6 +207,15 @@ setReadOnly( ns, 'flatten3dBy', require( '@stdlib/array/base/flatten3d-by' ) );
 */
 setReadOnly( ns, 'flatten4d', require( '@stdlib/array/base/flatten4d' ) );
 
+/**
+* @name flatten4dBy
+* @memberof ns
+* @readonly
+* @type {Function}
+* @see {@link module:@stdlib/array/base/flatten4d-by}
+*/
+setReadOnly( ns, 'flatten4dBy', require( '@stdlib/array/base/flatten4d-by' ) );
+
 /**
 * @name flatten5d
 * @memberof ns

From 247f2c8e833e16859a7dcbe9f3bd7c39bdf0c3bb Mon Sep 17 00:00:00 2001
From: Athan Reines <kgryte@gmail.com>
Date: Fri, 28 Jul 2023 22:11:58 -0600
Subject: [PATCH 3/4] docs: fix description

---
 .../@stdlib/array/base/flatten2d-by/docs/repl.txt             | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/node_modules/@stdlib/array/base/flatten2d-by/docs/repl.txt b/lib/node_modules/@stdlib/array/base/flatten2d-by/docs/repl.txt
index 6c3d75f1be2..a46014b9dc5 100644
--- a/lib/node_modules/@stdlib/array/base/flatten2d-by/docs/repl.txt
+++ b/lib/node_modules/@stdlib/array/base/flatten2d-by/docs/repl.txt
@@ -44,8 +44,8 @@
 
 
 {{alias}}.assign( x, shape, colex, out, stride, offset, clbk[, thisArg] )
-    Flattens a two-dimensional nested array and assigns elements to a provided
-    output array.
+    Flattens a two-dimensional nested array according to a callback function
+    and assigns elements to a provided output array.
 
     The function assumes that all nested arrays have the same length (i.e., the
     input array is *not* a ragged array).

From 1d3e0ad1c4cebb11e1b6caf66d551d9515c821cf Mon Sep 17 00:00:00 2001
From: Athan Reines <kgryte@gmail.com>
Date: Fri, 28 Jul 2023 22:15:27 -0600
Subject: [PATCH 4/4] docs: fix example

---
 lib/node_modules/@stdlib/array/base/flatten4d-by/README.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/node_modules/@stdlib/array/base/flatten4d-by/README.md b/lib/node_modules/@stdlib/array/base/flatten4d-by/README.md
index 6aa2e2e7acb..afb799faf9b 100644
--- a/lib/node_modules/@stdlib/array/base/flatten4d-by/README.md
+++ b/lib/node_modules/@stdlib/array/base/flatten4d-by/README.md
@@ -96,13 +96,13 @@ function scale( v ) {
 var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
 var out = new Float64Array( 4 );
 
-var y = flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0 );
+var y = flatten4dBy.assign( x, [ 2, 1, 1, 2 ], false, out, 1, 0, scale );
 // returns <Float64Array>[ 2, 4, 6, 8 ]
 
 var bool = ( y === out );
 // returns true
 
-y = flatten4dBy.assign( x, [ 2, 1, 1, 2 ], true, out, 1, 0 );
+y = flatten4dBy.assign( x, [ 2, 1, 1, 2 ], true, out, 1, 0, scale );
 // returns <Float64Array>[ 2, 6, 4, 8 ]
 ```