问题
I struggled for a while with the syntax to work for calculating a rolling function by group for a dask dataframe. The documentation is excellent, but in this case does not have an example.
The working version I have is as follows, from a csv that contains a text field with User ids and and x, y, and z column:
ddf = read_csv('./*.csv')
ddf.groupby(ddf.User).x.apply(lambda x: x.rolling(5).mean(), meta=('x', 'f8')).compute()
Is this the recommended syntax for rolling functions applied by group within dask DataFrames, or is there a recommended alternative?
回答1:
In order to retain the groups in the result:
ddf.groupby(by=User).apply(lambda df_g: df_g['x'].rolling(5).mean(), meta=('x', 'f8')).compute()
来源：https://stackoverflow.com/questions/42172130/dask-rolling-function-by-group-syntax