add average function

It would be nice to be able to do ds.average() to compute weighted averages (e.g. for geo data). Of course this would require the axes to be in a predictable order. Or to give a weight per dimension…

[shoyer]

I would suggest not using keyword arguments for weighted. Instead, just align based on the labels of the argument like regular xarray operations. So we’d write da.weighted(days_per_month(da.time)).mean()

[jhamman]

@MaximilianR has suggested a groupby/rolling-like interface to weighted reductions.

da.weighted(weights=ds.dim).mean()
# or maybe
da.weighted(time=days_per_month(da.time)).mean()

I really like this idea, as does @shoyer. I’m going to close my PR in hopes of this becoming reality.