use engine flox if array is ordered?

[mathause]

I find it a bit unfortunate that a quite common case (ordered groups) is 5-15 times slower with flox installed than without (pydata/xarray#7730). One option is to prefer engine="flox" if group_idx is ordered.

Is that something that could be considered? Or would that cause problem for the duck array support as discussed in engines?

I thought about opening an issue in numpy-groupies to add reduceat but maybe it's more relevant here.

[dcherian]

Yes we could use engine=None by default and check for sortedness of group_idx here:

flox/flox/core.py

Line 777 in bf49017

group_idx = group_idx.reshape(-1)

I use this check already:

flox/flox/aggregate_flox.py

Line 43 in bf49017

if (len(uniques) == size) and (uniques == np.arange(size, like=array)).all():

This would be a nice PR!

[dcherian]

Sorry I meant

flox/flox/aggregate_flox.py

Line 13 in bf49017

issorted = (group_idx[:-1] <= group_idx[1:]).all()