Documentation improvements

doc/whats-new.rst

@@ -30,6 +30,11 @@ Documentation
 - Add examples for :py:meth:`Dataset.swap_dims` and :py:meth:`DataArray.swap_dims`.
   By `Justus Magin <https://github.com/keewis>`_.
 
+- Add examples for :py:meth:`align`, :py:meth:`merge`, :py:meth:`combine_by_coords`, 
+  :py:meth:`full_like`, :py:meth:`zeros_like`, :py:meth:`ones_like`, :py:meth:`Dataset.pipe`, 
+  :py:meth:`Dataset.assign`, :py:meth:`Dataset.reindex`, :py:meth:`Dataset.fillna`.
+  By `Anderson Banihirwe <https://github.com/andersy005>`_.
+
 .. _whats-new.0.13.0:
 
 v0.13.0 (17 Sep 2019)

xarray/core/alignment.py

@@ -116,6 +116,136 @@ def align(
     ValueError
         If any dimensions without labels on the arguments have different sizes,
         or a different size than the size of the aligned dimension labels.
+
+    Examples
+    --------
+
+    >>> import xarray as xr
+    >>> x = xr.DataArray([[25, 35], [10, 24]], dims=('lat', 'lon'),
+    ...              coords={'lat': [35., 40.], 'lon': [100., 120.]})
+    >>> y = xr.DataArray([[20, 5], [7, 13]], dims=('lat', 'lon'),
+    ...              coords={'lat': [35., 42.], 'lon': [100., 120.]})
+
+    >>> x
+    <xarray.DataArray (lat: 2, lon: 2)>
+    array([[25, 35],
+           [10, 24]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0
+    * lon      (lon) float64 100.0 120.0
+
+    >>> y
+    <xarray.DataArray (lat: 2, lon: 2)>
+    array([[20,  5],
+           [ 7, 13]])
+    Coordinates:
+    * lat      (lat) float64 35.0 42.0
+    * lon      (lon) float64 100.0 120.0
+
+    >>> a, b = xr.align(x, y)
+    >>> a
+    <xarray.DataArray (lat: 1, lon: 2)>
+    array([[25, 35]])
+    Coordinates:
+    * lat      (lat) float64 35.0
+    * lon      (lon) float64 100.0 120.0
+    >>> b
+    <xarray.DataArray (lat: 1, lon: 2)>
+    array([[20,  5]])
+    Coordinates:
+    * lat      (lat) float64 35.0
+    * lon      (lon) float64 100.0 120.0
+
+    >>> a, b = xr.align(x, y, join='outer')
+    >>> a
+    <xarray.DataArray (lat: 3, lon: 2)>
+    array([[25., 35.],
+           [10., 24.],
+           [nan, nan]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0 42.0
+    * lon      (lon) float64 100.0 120.0
+    >>> b
+    <xarray.DataArray (lat: 3, lon: 2)>
+    array([[20.,  5.],
+           [nan, nan],
+           [ 7., 13.]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0 42.0
+    * lon      (lon) float64 100.0 120.0
+
+    >>> a, b = xr.align(x, y, join='outer', fill_value=-999)
+    >>> a
+    <xarray.DataArray (lat: 3, lon: 2)>
+    array([[  25,   35],
+           [  10,   24],
+           [-999, -999]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0 42.0
+    * lon      (lon) float64 100.0 120.0
+    >>> b
+    <xarray.DataArray (lat: 3, lon: 2)>
+    array([[  20,    5],
+           [-999, -999],
+           [   7,   13]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0 42.0
+    * lon      (lon) float64 100.0 120.0
+
+    >>> a, b = xr.align(x, y, join='left')
+    >>> a
+    <xarray.DataArray (lat: 2, lon: 2)>
+    array([[25, 35],
+           [10, 24]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0
+    * lon      (lon) float64 100.0 120.0
+    >>> b
+    <xarray.DataArray (lat: 2, lon: 2)>
+    array([[20.,  5.],
+           [nan, nan]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0
+    * lon      (lon) float64 100.0 120.0
+
+    >>> a, b = xr.align(x, y, join='right')
+    >>> a
+    <xarray.DataArray (lat: 2, lon: 2)>
+    array([[25., 35.],
+           [nan, nan]])
+    Coordinates:
+    * lat      (lat) float64 35.0 42.0
+    * lon      (lon) float64 100.0 120.0
+    >>> b
+    <xarray.DataArray (lat: 2, lon: 2)>
+    array([[20,  5],
+           [ 7, 13]])
+    Coordinates:
+    * lat      (lat) float64 35.0 42.0
+    * lon      (lon) float64 100.0 120.0
+
+    >>> a, b = xr.align(x, y, join='exact')
+    Traceback (most recent call last):
+    ...
+        "indexes along dimension {!r} are not equal".format(dim)
+    ValueError: indexes along dimension 'lat' are not equal
+
+    >>> a, b = xr.align(x, y, join='override')
+    >>> a
+    <xarray.DataArray (lat: 2, lon: 2)>
+    array([[25, 35],
+           [10, 24]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0
+    * lon      (lon) float64 100.0 120.0
+    >>> b
+    <xarray.DataArray (lat: 2, lon: 2)>
+    array([[20,  5],
+           [ 7, 13]])
+    Coordinates:
+    * lat      (lat) float64 35.0 40.0
+    * lon      (lon) float64 100.0 120.0
+
     """
     if indexes is None:
         indexes = {}

xarray/core/combine.py

@@ -393,7 +393,7 @@ def combine_nested(
     --------
 
     A common task is collecting data from a parallelized simulation in which
-    each processor wrote out to a separate file. A domain which was decomposed
+    each process wrote out to a separate file. A domain which was decomposed
     into 4 parts, 2 each along both the x and y axes, requires organising the
     datasets into a doubly-nested list, e.g:
 
@@ -505,8 +505,7 @@ def combine_by_coords(
     ----------
     datasets : sequence of xarray.Dataset
         Dataset objects to combine.
-    compat : {'identical', 'equals', 'broadcast_equals',
-              'no_conflicts', 'override'}, optional
+    compat : {'identical', 'equals', 'broadcast_equals', 'no_conflicts', 'override'}, optional
         String indicating how to compare variables of the same name for
         potential conflicts:
 
@@ -520,9 +519,21 @@ def combine_by_coords(
           of all non-null values.
         - 'override': skip comparing and pick variable from first dataset
     data_vars : {'minimal', 'different', 'all' or list of str}, optional
-        Details are in the documentation of concat
+        These data variables will be concatenated together:
+
+        * 'minimal': Only data variables in which the dimension already
+          appears are included.
+        * 'different': Data variables which are not equal (ignoring
+          attributes) across all datasets are also concatenated (as well as
+          all for which dimension already appears). Beware: this option may
+          load the data payload of data variables into memory if they are not
+          already loaded.
+        * 'all': All data variables will be concatenated.
+        * list of str: The listed data variables will be concatenated, in
+          addition to the 'minimal' data variables.
+        If objects are DataArrays, `data_vars` must be 'all'.
     coords : {'minimal', 'different', 'all' or list of str}, optional
-        Details are in the documentation of concat
+        As per the 'data_vars' kwarg, for coords.
     fill_value : scalar, optional
         Value to use for newly missing values
     join : {'outer', 'inner', 'left', 'right', 'exact'}, optional
@@ -556,29 +567,91 @@ def combine_by_coords(
     they are concatenated based on the values in their dimension coordinates,
     not on their position in the list passed to `combine_by_coords`.
 
+    >>> import numpy as np
+    >>> import xarray as xr
+
+    >>> x1 = xr.Dataset(
+    ...     {
+    ...         "temperature": (("y", "x"), 20 * np.random.rand(6).reshape(2, 3)),
+    ...         "precipitation": (("y", "x"), np.random.rand(6).reshape(2, 3)),
+    ...     },
+    ...     coords={"y": [0, 1], "x": [10, 20, 30]},
+    ... )
+    >>> x2 = xr.Dataset(
+    ...     {
+    ...         "temperature": (("y", "x"), 20 * np.random.rand(6).reshape(2, 3)),
+    ...         "precipitation": (("y", "x"), np.random.rand(6).reshape(2, 3)),
+    ...     },
+    ...     coords={"y": [2, 3], "x": [10, 20, 30]},
+    ... )
+    >>> x3 = xr.Dataset(
+    ...     {
+    ...         "temperature": (("y", "x"), 20 * np.random.rand(6).reshape(2, 3)),
+    ...         "precipitation": (("y", "x"), np.random.rand(6).reshape(2, 3)),
+    ...     },
+    ...     coords={"y": [2, 3], "x": [40, 50, 60]},
+    ... )
+
     >>> x1
     <xarray.Dataset>
-    Dimensions:         (x: 3)
-    Coords:
-      * position        (x) int64   0 1 2
+    Dimensions:        (x: 3, y: 2)
+    Coordinates:
+    * y              (y) int64 0 1
+    * x              (x) int64 10 20 30
     Data variables:
-        temperature     (x) float64 11.04 23.57 20.77 ...
+        temperature    (y, x) float64 1.654 10.63 7.015 2.543 13.93 9.436
+        precipitation  (y, x) float64 0.2136 0.9974 0.7603 0.4679 0.3115 0.945
 
     >>> x2
     <xarray.Dataset>
-    Dimensions:         (x: 3)
-    Coords:
-      * position        (x) int64   3 4 5
+    Dimensions:        (x: 3, y: 2)
+    Coordinates:
+    * y              (y) int64 2 3
+    * x              (x) int64 10 20 30
+    Data variables:
+        temperature    (y, x) float64 9.341 0.1251 6.269 7.709 8.82 2.316
+        precipitation  (y, x) float64 0.1728 0.1178 0.03018 0.6509 0.06938 0.3792
+
+    >>> x3
+    <xarray.Dataset>
+    Dimensions:        (x: 3, y: 2)
+    Coordinates:
+    * y              (y) int64 2 3
+    * x              (x) int64 40 50 60
     Data variables:
-        temperature     (x) float64 6.97 8.13 7.42 ...
+        temperature    (y, x) float64 2.789 2.446 6.551 12.46 2.22 15.96
+        precipitation  (y, x) float64 0.4804 0.1902 0.2457 0.6125 0.4654 0.5953
 
-    >>> combined = xr.combine_by_coords([x2, x1])
+    >>> xr.combine_by_coords([x2, x1])
     <xarray.Dataset>
-    Dimensions:         (x: 6)
-    Coords:
-      * position        (x) int64   0 1 2 3 4 5
+    Dimensions:        (x: 3, y: 4)
+    Coordinates:
+    * x              (x) int64 10 20 30
+    * y              (y) int64 0 1 2 3
     Data variables:
-        temperature     (x) float64 11.04 23.57 20.77 ...
+        temperature    (y, x) float64 1.654 10.63 7.015 2.543 ... 7.709 8.82 2.316
+        precipitation  (y, x) float64 0.2136 0.9974 0.7603 ... 0.6509 0.06938 0.3792
+
+    >>> xr.combine_by_coords([x3, x1])
+    <xarray.Dataset>
+    Dimensions:        (x: 6, y: 4)
+    Coordinates:
+    * x              (x) int64 10 20 30 40 50 60
+    * y              (y) int64 0 1 2 3
+    Data variables:
+        temperature    (y, x) float64 1.654 10.63 7.015 nan ... nan 12.46 2.22 15.96
+        precipitation  (y, x) float64 0.2136 0.9974 0.7603 ... 0.6125 0.4654 0.5953
+
+    >>> xr.combine_by_coords([x3, x1], join='override')
+    <xarray.Dataset>
+    Dimensions:        (x: 3, y: 4)
+    Coordinates:
+    * x              (x) int64 10 20 30
+    * y              (y) int64 0 1 2 3
+    Data variables:
+    temperature    (y, x) float64 1.654 10.63 7.015 2.543 ... 12.46 2.22 15.96
+    precipitation  (y, x) float64 0.2136 0.9974 0.7603 ... 0.6125 0.4654 0.5953
+
     """
 
     # Group by data vars