Re: Python slices in Scheme

[Zelphir Kaltstahl]

On 6/19/23 18:36, lloda wrote:
> My library guile-newra (1) has quite general multidimensional array slicing. 
> The indices can be linear ranges or arbitrary integer arrays and they can have 
> any rank. You can also use the indexed array as write target. If all the 
> indices are linear ranges then the operation is done without copies. It also 
> has placeholders, so you can skip axes, like :  and ... in numpy. guile-newra's 
> arrays are applicative, so you can do (thearray firstindex secondindex ...), 
> without special brackets.
>
> You need wrappers to use it with Guile's native array types, so it may not be 
> as convenient. Or maybe you don't need to handle arbitrary rank, then it might 
> not be the best option. It's also far from finished, although the stuff I 
> mentioned above does work.
>
> I didn't adopt Pythons -1 = end convention because in Guile arrays can have any 
> base index, not necessarily 0 (whether that's a good idea or not).
>
> (1)https://lloda.github.io/guile-newra/#Slicing  
> <https://lloda.github.io/guile-newra/#Slicing>
> https://github.com/lloda/guile-newra/  <https://github.com/lloda/guile-newra/>
> https://notabug.org/lloda/guile-newra  <https://notabug.org/lloda/guile-newra>

This reminds me of something I did for last year's advent of code: 
https://notabug.org/ZelphirKaltstahl/advent-of-code-2022/src/931399414114380121df547e6bec4dfba35772a4/day-15/array-helpers.scm

This contains notably the following functions:

(1) array-next-index: iterate through an array of arbitrary rank, going from 
index to index

(2) array-cell-ref-vec: allows partial referencing of array elements, for 
example:

~~~~
(array-cell-ref-vec #2((1 2 3) (4 5 6)) #(1))
=> #1(4 5 6)
(array-cell-ref-vec #3(((1 2 3) (4 5 6)) ((1 2 3) (4 5 6))) #(1))
=> #2((1 2 3) (4 5 6))
(array-cell-ref-vec #3(((1 2 3) (4 5 6)) ((1 2 3) (4 5 6))) #(1 1))
=> #1(4 5 6)
(array-cell-ref-vec #3(((1 2 3) (4 5 6)) ((1 2 3) (4 5 6))) #(1 1 1))
=> 5
~~~~

(3) array-index-of: find the index of the first element satisfying predicate 
(using array-next-index)

(4) array-indices-of: find all indices of elements satisfying a predicate (using 
array-next-index)

Regards,
Zelphir

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