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Impl NdIndex<IxDyn> for &Vec<Ix> and Vec<Ix>#1146

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bderrett wants to merge1 commit intorust-ndarray:master
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@bderrettbderrett commentedJan 18, 2022•
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This change attempts to improve the ergonomics of indexing dynamic dimension arrays.

Let's say we have:

letmut a =ArrayD::<f32>::zeros(vec![1,2]);let index =vec![0,0];

(Of course, in practice, the number of dims is dynamic.)

Then currently we can't doa[&index] = 1.0 ora[index] = 1.0. Instead we seem to need to do

let r:&[usize] =&index;a[r] =1.0;

This change makes the first two methods of indexing possible.

I'm new tondarray, so there may be a discussion on this somewhere that I haven't seen. The new impls were created by copying the impl of &[Ix] (for &Vec) and by modifying the impl of &[Ix] (for Vec).

I can add tests for this if it looks useful?

@jturner314
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Thanks for the PR. I agree that it may be worth addingIndex implementations forVec<usize> and&Vec<usize>; there isn't much downside. Alternatively, we could add implementations forVec<usize> and&T where T: NdIndex<IxDyn>.

@bluss What do you think?

Fwiw, this currently works withndarray:

letmut a =ArrayD::<f32>::zeros(vec![1,2]);let index =vec![0,0];a[&*index] =1.0;

(Note the extra* to use theVec'sDeref implementation.)

Ifindex is&Vec<usize>, it's a bit more awkward:a[&**index] = 1.0 ora[index.as_slice()] = 1.0.

Regarding the implementation -- I'd suggest converting to&[usize] and using the existingNdIndex<IxDyn> for &'a [Ix] implementation. (Look atNdIndex<IxDyn> for &'a IxDyn for a similar case.)

@bderrett
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Many thanks for the comments. The PR now adds implementations forVec<usize> and&T where T: NdIndex<IxDyn>.

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