xarray.Dataset.groupby

Dataset.groupby(group, squeeze: bool = True)

Returns a GroupBy object for performing grouped operations.

Parameters
groupstr, DataArray or IndexVariable

Array whose unique values should be used to group this array. If a string, must be the name of a variable contained in this dataset.

squeezeboolean, optional

If “group” is a dimension of any arrays in this dataset, squeeze controls whether the subarrays have a dimension of length 1 along that dimension or if the dimension is squeezed out.

Returns
groupedGroupBy

A GroupBy object patterned after pandas.GroupBy that can be iterated over in the form of (unique_value, grouped_array) pairs.

Examples

Calculate daily anomalies for daily data:

>>> da = xr.DataArray(np.linspace(0, 1826, num=1827),
...                   coords=[pd.date_range('1/1/2000', '31/12/2004',
...                           freq='D')],
...                   dims='time')
>>> da
<xarray.DataArray (time: 1827)>
array([0.000e+00, 1.000e+00, 2.000e+00, ..., 1.824e+03, 1.825e+03, 1.826e+03])
Coordinates:
  * time     (time) datetime64[ns] 2000-01-01 2000-01-02 2000-01-03 ...
>>> da.groupby('time.dayofyear') - da.groupby('time.dayofyear').mean('time')
<xarray.DataArray (time: 1827)>
array([-730.8, -730.8, -730.8, ...,  730.2,  730.2,  730.5])
Coordinates:
  * time       (time) datetime64[ns] 2000-01-01 2000-01-02 2000-01-03 ...
    dayofyear  (time) int64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 ...