diff --git a/xarray/core/parallel.py b/xarray/core/parallel.py index dd6c67338d8..e4fb5803191 100644 --- a/xarray/core/parallel.py +++ b/xarray/core/parallel.py @@ -154,6 +154,48 @@ def map_blocks( -------- dask.array.map_blocks, xarray.apply_ufunc, xarray.Dataset.map_blocks, xarray.DataArray.map_blocks + + Examples + -------- + + Calculate an anomaly from climatology using ``.groupby()``. Using + ``xr.map_blocks()`` allows for parallel operations with knowledge of ``xarray``, + its indices, and its methods like ``.groupby()``. + + >>> def calculate_anomaly(da, groupby_type='time.month'): + ... # Necessary workaround to xarray's check with zero dimensions + ... # https://github.com/pydata/xarray/issues/3575 + ... if sum(da.shape) == 0: + ... return da + ... gb = da.groupby(groupby_type) + ... clim = gb.mean(dim='time') + ... return gb - clim + >>> time = xr.cftime_range('1990-01', '1992-01', freq='M') + >>> np.random.seed(123) + >>> array = xr.DataArray(np.random.rand(len(time)), + ... dims="time", coords=[time]).chunk() + >>> xr.map_blocks(calculate_anomaly, array).compute() + + array([ 0.12894847, 0.11323072, -0.0855964 , -0.09334032, 0.26848862, + 0.12382735, 0.22460641, 0.07650108, -0.07673453, -0.22865714, + -0.19063865, 0.0590131 , -0.12894847, -0.11323072, 0.0855964 , + 0.09334032, -0.26848862, -0.12382735, -0.22460641, -0.07650108, + 0.07673453, 0.22865714, 0.19063865, -0.0590131 ]) + Coordinates: + * time (time) object 1990-01-31 00:00:00 ... 1991-12-31 00:00:00 + + Note that one must explicitly use ``args=[]`` and ``kwargs={}`` to pass arguments + to the function being applied in ``xr.map_blocks()``: + + >>> xr.map_blocks(calculate_anomaly, array, kwargs={'groupby_type': 'time.year'}) + + array([ 0.15361741, -0.25671244, -0.31600032, 0.008463 , 0.1766172 , + -0.11974531, 0.43791243, 0.14197797, -0.06191987, -0.15073425, + -0.19967375, 0.18619794, -0.05100474, -0.42989909, -0.09153273, + 0.24841842, -0.30708526, -0.31412523, 0.04197439, 0.0422506 , + 0.14482397, 0.35985481, 0.23487834, 0.12144652]) + Coordinates: + * time (time) object 1990-01-31 00:00:00 ... 1991-12-31 00:00:00 """ def _wrapper(func, obj, to_array, args, kwargs):