GH-44393: [C++][Compute] Placement vector functions #44394
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Hi, @felipecrv @pitrou . Could you help to review this? I think this is a necessary building block for special forms (#41094 (comment)). Much appreciated! |
zanmato1984
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@zanmato1984 I'm not doing code reviews with the same frequency lately, but I might take a look at this one during the week. |
felipecrv
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Oct 31, 2024
| /// | ||
| /// For indices[i] = x, reverse_indices[x] = i. And reverse_indices[x] = null if x does | ||
| /// not appear in the input indices. For indices[i] = x where x < 0 or x >= output_length, | ||
| /// it is ignored. If multiple indices point to the same value, the last one is used. |
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I think this explanation is confusing, but we can work on this later.
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Rationale for this change
For background please see #44393.
When implementing the "scatter" function requested in #44393, I found it also useful to make it a public vector API. After a painful thinking, I decided to name it "permute". And when implementing permute, I found it fairly easy to implement it by first computing the "reverse indices" of the positions, and then invoking the existing "take", where I think "reverse_indices" itself can also be a useful public vector API. Thus the PR categorized them as "placement functions".
What changes are included in this PR?
Implement placement API
reverse_indicesandpermute, wherepermute(values, indices)is implemented astake(values, reverse_indices(indices)).I also put a small UT
Permute.IfElsedemonstrating howpermutecan serve as a building block of implementing special forms.Are these changes tested?
UT included.
Are there any user-facing changes?
Yes, new public APIs added. Documents updated.