Indexing explanations cleanup #5791
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| * There are only integer array indices so that no subspace exists. | ||
| * View based and advanced indexing is mixed. In this case there is a "subspace" | ||
| defined by the view based indexing and having the same functionality. For | ||
| example for ``arr[[1, 2, 3], :]`` the subspace is defined by ``arr[0, :]``. |
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@seberg I still don't understand the arr[0, :] subspace bit.
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Oh, you worked on this. Thanks, though I hate to pass it on.
Well, it was supposed to say that you iterate the advanced indices and what is left is the "subspace" which moves around:
arr = np.ones((3, 4, 5))
arr[indx1, :, indx2]
Then this is much like:
res[0, :] = arr[indx1[0], :, indx2[0]]
res[1, :] = arr[indx1[1], :, indx2[1]]
res[2, :] = arr[indx1[2], :, indx2[2]]
…
If you look at the strides, you get that each of that is:
arr[0, :, 0] + pointer_offset_according_to_arrays
so that arr[0, :, 0] is the "subspace" (might be invalid, but ignore that) and the offset to where we are right now is defined by the current advamced index. Not sure if this all helps, but maybe the long example where you just unravel the advanced indexing helps a lot.
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I wanted to get something in for 1.10 and figured you could take it up again. Feel free to pull this and close it if you get inspired.
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OK, I've rewritten that bit and replaced "subspace" by "subarray".
Basic cleanup of the new indexing documentation. Also replace "subspace" by "subarray" and try to clarify mixed advanced and view indexing. [skip ci]
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@seberg Putting this in as a start. Finish it up when you have the time. |
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OK, thanks.
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Small fixes to @seberg work in #4331.