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at

Return an ndarray element.

Installation

npm install @stdlib/ndarray-at

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var at = require( '@stdlib/ndarray-at' );

at( x[, ...indices] )

Returns an ndarray element.

var array = require( '@stdlib/ndarray-array' );

var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
// returns <ndarray>

var v = at( x, 0, 0 );
// returns 1

v = at( x, 0, 1 );
// returns 2

v = at( x, 1, 0 );
// returns 3

v = at( x, 1, 1 );
// returns 4

The function accepts the following arguments:

• x: input ndarray.
• indices: index arguments. The number of index arguments must equal the number of dimensions.

Notes

• If provided out-of-bounds indices, the function always returns undefined.

  var array = require( '@stdlib/ndarray-array' );
  
  var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
  // returns <ndarray>
  
  var v = at( x, 10, 20 );
  // returns undefined

• Negative indices are resolved relative to the last element along the respective dimension, with the last element corresponding to -1.

  var array = require( '@stdlib/ndarray-array' );
  
  var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
  // returns <ndarray>
  
  var v = at( x, -1, -1 );
  // returns 4
  
  v = at( x, -2, -2 );
  // returns 1

Examples

var cartesianProduct = require( '@stdlib/array-cartesian-product' );
var zeroTo = require( '@stdlib/array-zero-to' );
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var array = require( '@stdlib/ndarray-array' );
var at = require( '@stdlib/ndarray-at' );

// Define a two-dimensional array:
var shape = [ 5, 5 ];
var x = array( discreteUniform( 25, -100, 100 ), {
    'shape': shape
});

// Define lists of dimension indices:
var i0 = zeroTo( shape[ 0 ], 'generic' );
var i1 = zeroTo( shape[ 1 ], 'generic' );

// Create a list of index pairs:
var indices = cartesianProduct( i0, i1 );

// Print array contents...
var idx;
var i;
for ( i = 0; i < x.length; i++ ) {
    idx = indices[ i ];
    console.log( 'x[%d,%d] = %d', idx[ 0 ], idx[ 1 ], at( x, idx[ 0 ], idx[ 1 ] ) );
}

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See Also

• @stdlib/ndarray-array: multidimensional arrays.
• @stdlib/ndarray-slice: return a read-only view of an input ndarray.

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.