Investigate interfaces to monthly and annual temporal averaging

[agstephens]

Description

We are looking at adding monthly and annual averaging to the roocs stack. Carsten has made a suggestion in this PR:

#191

Task

@ellesmith88 Please can you do some looking around in similar code stacks/standards to see how interfaces to these types of temporal averages are described (like you did before when we defined the main interface to the subset operation). It would be good for us to learn from other approaches (although we may still choose our own :-)

Please document what you find in this issue.

[ellesmith88]

I've put together a spreadsheet of examples I was able to find: https://docs.google.com/spreadsheets/d/1VLkIxFvYlGPqO-MW1pNaHKXuBFTQNMbi4KZrNG2RmWo/edit?usp=sharing

I couldn't think of or find any more stacks/standards to look at for temporal averaging, if there are others let me know and I'll look into them :)

[agstephens]

Hi Elle,
This looks great.
Thanks

[agstephens]

After discussions with the C3S team, we are considering:

resample(collection, dims="time", freq="month", how="mean")

or

aggregate(collection, dims="time", freq="month", how="mean")

The resample operation/method is common to xarray, pandas and cds-toolbox. The aggregate operation/method exists in xarray.

[agstephens]

Or:

clisops.ops.average::average(ds, dims="time", freq="month")

or:

clisops.ops.average::average_time(ds, freq="month")

[agstephens]

Side discussion...

• ideally, clisops.core would contain numerous functions that all do 1 thing - and you can chain them in a workflow because they are all operating on dask.delayed objects
• maybe we should refactor functions like subset_bbox so that the time and level parts are excluded
  • then clisops.ops.subset can decide which functions are called

If we refactored as above, then it would make more sense to write clisops.core.average::average(ds, dims=["time", "longitude"], freq="month") knowing that clisops.ops.average::average(...) could offer more functionality (or maybe not).

Note refactoring issue: roocs/clisops#114

Ouranos support this suggestion: clisops.core has single/specific functions that can be chained together (with delayed compute).

[agstephens]

Decision! We will start by implementing this:

clisops.core.average::average_time(ds, freq="month"|"year")

and...

clisops.ops.average::average_time(ds, freq="month"|"year")

[agstephens]

@ellesmith88 please have a look.