xarray.where

xarray.where(cond, x, y)

Return elements from x or y depending on cond.

Performs xarray-like broadcasting across input arguments.

Parameters
  • cond (scalar, array, Variable, DataArray or Dataset with boolean dtype) – When True, return values from x, otherwise returns values from y.

  • y (x,) – Values from which to choose. All dimension coordinates on these objects must be aligned with each other and with cond.

Returns

  • In priority order (Dataset, DataArray, Variable or array, whichever)

  • type appears as an input argument.

Examples

>>> import xarray as xr
>>> import numpy as np
>>> x = xr.DataArray(0.1 * np.arange(10), dims=['lat'],
...                  coords={'lat': np.arange(10)}, name='sst')
>>> x
<xarray.DataArray 'sst' (lat: 10)>
array([0. , 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9])
Coordinates:
* lat      (lat) int64 0 1 2 3 4 5 6 7 8 9
>>> xr.where(x < 0.5, x,  100*x)
<xarray.DataArray 'sst' (lat: 10)>
array([ 0. ,  0.1,  0.2,  0.3,  0.4, 50. , 60. , 70. , 80. , 90. ])
Coordinates:
* lat      (lat) int64 0 1 2 3 4 5 6 7 8 9
>>> >>> y = xr.DataArray(
...     0.1 * np.arange(9).reshape(3, 3),
...     dims=["lat", "lon"],
...     coords={"lat": np.arange(3), "lon": 10 + np.arange(3)},
...     name="sst",
... )
>>> y
<xarray.DataArray 'sst' (lat: 3, lon: 3)>
array([[0. , 0.1, 0.2],
       [0.3, 0.4, 0.5],
       [0.6, 0.7, 0.8]])
Coordinates:
* lat      (lat) int64 0 1 2
* lon      (lon) int64 10 11 12
>>> xr.where(y.lat < 1, y, -1)
<xarray.DataArray (lat: 3, lon: 3)>
array([[ 0. ,  0.1,  0.2],
       [-1. , -1. , -1. ],
       [-1. , -1. , -1. ]])
Coordinates:
* lat      (lat) int64 0 1 2
* lon      (lon) int64 10 11 12
>>> cond = xr.DataArray([True, False], dims=['x'])
>>> x = xr.DataArray([1, 2], dims=['y'])
>>> xr.where(cond, x, 0)
<xarray.DataArray (x: 2, y: 2)>
array([[1, 2],
       [0, 0]])
Dimensions without coordinates: x, y

See also

numpy.where()

corresponding numpy function

Dataset.where(), DataArray.where()