GroupBy like API for resample

Since we wrote resample in xarray, pandas updated resample to have a groupyby-like API (e.g., df.resample('24H').mean() vs. the old df.resample('24H') that uses the mean by default).

It would be nice to redo the xarray resample API to match, e.g., ds.resample(time='24H').mean() vs ds.resample('time', '24H'). This would solve a few use cases, including grouped-resample arithmetic, iterating over groups and (mostly) take care of the need for pd.TimeGrouper support (https://github.com/pydata/xarray/issues/364). If we use **kwargs for matching dimension names, this could be done with a minimally painful deprecation cycle.

[darothen]

@MaximilianR Oh, the interface is easy enough to do, even maintaining backwards-compatibility (already have that working). I was considering going the route done with GroupBy and the classes that compose it, like DatasetGroupBy… basically, we just record the wanted resampling dimension and inject the grouping/resampling operations we want. Also adds the ability to specialize methods like .first() and .last(), which is done under the current implementation.

But… if there’s a simpler way, that might be preferable!

[shoyer]

I think this could be done with minimal GroupBy subclasses to supply the default dimension argument for aggregation functions. All the machinery on groupby should already be there. On Wed, Feb 15, 2017 at 10:59 AM Daniel Rothenberg [e-mail] wrote:

@MaximilianR https://github.com/MaximilianR Oh, the interface is easy enough to do, even maintaining backwards-compatibility (already have that working). I was considering going the route done with GroupBy https://github.com/pydata/xarray/blob/93d6963315026f87841c7cf39cc39bb78f555345/xarray/core/groupby.py#L165 and the classes that compose it, like DatasetGroupBy https://github.com/pydata/xarray/blob/93d6963315026f87841c7cf39cc39bb78f555345/xarray/core/groupby.py#L586… basically, we just record the wanted resampling dimension and inject the grouping/resampling operations we want. Also adds the ability to specialize methods like .first() and .last(), which is done under the current implementation.

But… if there’s a simpler way, that might be preferable!

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