Checked Subtract Support

[benburk]

Running the following code...

let z: Array1<u32> = arr1(&[1,0,1]) - arr1(&[0,1,0]);

...causes a panic with attempt to subtract with overflow'

Would it be possible to get support for something such as

let z: Array1<u32> =  arr1(&[1,0,1]).checked_sub(arr1(&[0,1,0])).unwrap();

or is there an alternative approach one can suggest?

[bluss]

we discussed wrapping here: https://github.com/rust-ndarray/ndarray/pull/1107#issuecomment-974896229 also needs a design, so nothing implemented yet. I guess this is a bit of a similar issue, yet it needs a quite different solution.

What's the use case here? What motivates wanting a checked_sub if you unwrap it?

[benburk]

The code is just for illustrative purposes. In actuality, it gives one the ability to handle the Option however one likes, as in any other usage of the regular checked_sub. In my specific case, I was looking to do something like this

let z: HashMap<Array2<u32>, u32> = my_hashmap
            .into_iter()
            .map(|(k, v): (Array2<u32>, u32)| (k.checked_sub(state), v))
            .flatten()
            .collect();

If you could propose a clean alternative, perhaps by comparing the two arrays before doing the subtraction, that would be appreciated!