MAINT: extend delete single value optimization

[DevinShanahan]

Allow arrays of shape (1,) for np.delete's obj parameter to utilize the optimization for a single value. See #16685.

In [2]: arr = np.arange(3000000).reshape(1000, 3000)      
                      
In [3]: %timeit np.delete(arr, obj=0, axis=1)                                   
6.91 ms ± 352 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

In [4]: %timeit np.delete(arr, obj=[0], axis=1)                                 
6.72 ms ± 245 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

In [5]: zero = np.array([0])                                                    

In [6]: %timeit np.delete(arr, obj=zero, axis=1)                                
6.77 ms ± 242 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

[mattip]

Closes #16685

[eric-wieser]

item() makes me worry here...

[eric-wieser]

Does this patch change the behavior of np.delete(np.arange(10), np.array([1], dtype=object))?

[eric-wieser]

I think obj = obj.reshape(()) would avoid that shortcoming - please add a test!

[DevinShanahan]

Could your clarify the behavior you are concerned about for np.delete(np.arange(10), np.array([1], dtype=object)). I will change it to obj = obj.reshape(()) either way but the behavior appears the same to me. What would you like to see in the test?

Also, is there anything else you would like to see tested?

More tests needed

[InessaPawson]

@DevinShanahan Do you think you could finish this PR? It would be nice to fix #16685.

[DevinShanahan]

@InessaPawson Yes, I will try to complete this as soon as possible.

[DevinShanahan]

@InessaPawson I've re-requested a review, anything else you need from me on this at this time?

[InessaPawson]

@DevinShanahan Thank you for updating the PR! We will review it shortly.

[mattip]

Thanks @DevinShanahan

[InessaPawson]

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[seberg]

This PR broke bolean array inputs, see gh-21840 (at least I am practically certain). Unfortunately, we need to either carefully check all the paths the "integer array" paths (which seem to accept booleans arrays now) or simply revert it and give it another shot some other time.