Views with non-fixed steps

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
rust
Domain
data

Research direction

Start by reading the ndarray APIs shown in the issue: select, s!, Axis, and Zip, and compare their view and copying behavior. The work is done when the project has a documented way to view arbitrary indices without copying, or clearly establishes that the existing approach is required.

Written by the indexing model from the issue text.

Description

I work with big 4D images, often iterating on Axis(3) to modify it or create a new image. In some cases, I need to iterate only on some indices:

let dwi = Array4::wathever // Loaded from disk
let dwi_indices = vec![2, 3, 10, 13, 17, 21 ...]; // Calculated from dwi
let mut output = Array4::zeros((dwi.dim().0, dwi.dim().1, dwi.dim().2, dwi_indices.len()));
Zip::from(&dwi_indices).and(output.axis_iter_mut(Axis(3))).apply(|&i, volume| {
    let dwi = self.dwi.index_axis(Axis(3), i);
    volume.assign(...);
});

This method works and I can keep it but is there a way to ask for a view with the right indices? select is nice but it makes a copy of the data. s! asks for a step, which I can't give because it's "random". Anything like let dwi = dwi.slice(s![.., .., .., &self.dwi_indices]);?

Dominant language
Rust
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