ENH: add apply_along_axis

[paddyroddy]

Are there plans to support apply_along_axis?

• numpy
• cupy
• torch
• dask
• jax

[lucascolley]

@mdhaber I think I remember some past discussion on this? Maybe I'm getting mixed up with something else.

[mdhaber]

I don't remember specifically - I'd guess it was about how stats functions often rely on apply_along_axis to provide an axis argument or how the resampling tests use apply_along_axis if the user-specified statistic doesn't support an axis argument.
I can imagine this providing a speedup vs looping on some backends (even though it doesn't really with NumPy). If so, I think it would be valuable, and we'd use it.
Something that would make it much more useful is if the arr argument would support a tuple of arrays. Currently, we concatenate arrays along axis and then split each slice within func1d, but that's quite inefficient. (Dealing with higher dimensional core shapes is not as bad because we can typically reshape arr then undo in func1d.)