xarray_groupby_multiple_dims.py

import xarray as xr
import numpy as np

# create an example dataset
da = xr.DataArray(np.random.rand(10,30,40), dims=['time', 'lat', 'lon'])

# define a function to compute a linear trend of a timeseries
def linear_trend(x):
    pf = np.polyfit(x.time, x, 1)
    # we need to return a dataarray or else xarray's groupby won't be happy
    return xr.DataArray(pf[0])

# stack lat and lon into a single dimension called allpoints
stacked = da.stack(allpoints=['lat','lon'])
# apply the function over allpoints to calculate the trend at each point
trend = stacked.groupby('allpoints').apply(linear_trend)
# unstack back to lat lon coordinates
trend_unstacked = trend.unstack('allpoints')
  

How the xarray.polyfit different from this ?