Add dak.where

[lgray]

Fixes #127

[codecov-commenter]

Codecov Report

Merging #133 (3365e72) into main (78e5712) will decrease coverage by 0.03%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main     #133      +/-   ##
==========================================
- Coverage   95.72%   95.69%   -0.04%     
==========================================
  Files          18       18              
  Lines        1754     1765      +11     
==========================================
+ Hits         1679     1689      +10     
- Misses         75       76       +1     

Impacted Files	Coverage Δ
src/dask_awkward/lib/structure.py	96.22% <91.66%> (-0.30%)	⬇️

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[lgray]

It occurs to me that we could make it so the meta is known ahead of time because ak.where most often implies a return value of ?? * outer * structure * union[the,input,types], where the union type can be simplified. However, ak.where does not function on typetracers. Presently returns an error like this:

>>> ak.where((dx > 2)._meta, dx._meta, dx._meta)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/operations/ak_where.py", line 61, in where
    return _impl3(condition, x, y, mergebool, highlevel, behavior)
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/operations/ak_where.py", line 132, in _impl3
    out = ak._broadcasting.broadcast_and_apply(
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/_broadcasting.py", line 1022, in broadcast_and_apply
    out = apply_step(
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/_broadcasting.py", line 1001, in apply_step
    return continuation()
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/_broadcasting.py", line 723, in continuation
    outcontent = apply_step(
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/_broadcasting.py", line 1001, in apply_step
    return continuation()
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/_broadcasting.py", line 766, in continuation
    outcontent = apply_step(
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/_broadcasting.py", line 987, in apply_step
    result = action(
  File "/Users/lgray/miniforge3/lib/python3.9/site-packages/awkward/operations/ak_where.py", line 111, in action
    tags = ak.index.Index8((npcondition == 0).view(np.int8))
AttributeError: 'bool' object has no attribute 'view'

where dx is a dask-awkward array. @jpivarski do you think it would be possible to get ak.where to predict the return type based on a typetracer?

[jpivarski]

The above should now be fixed in Awkward main.

[lgray]

@jpivarski I confirm in Awkward main that dak.where no longer requires running the first chunk to determine array metadata and functions correctly on typetracers.

[lgray]

This should now pass CI if run, with the release of awkward 2.0.3!

[lgray]

Could someone kick this PR for tests? Thanks!

[martindurant]

Rerunning all tests

[martindurant]

(I think pushing an empty commit is actually the easiest way to do that!)

[lgray]

@martindurant the tests will not run automatically for me yet since I have not successfully completed a PR to this repository. Some branch/repository protection rule.