Best syntax for a diagonal and vertical slice

[Ilya Yaroshenko via Digitalmars-d-learn]

On Saturday, 22 July 2017 at 20:55:06 UTC, kerdemdemir wrote:
> We have awesome way for creating slices like:
>
>     a = new int[5];
>     int[] b = a[0..2];
>
> But what about if I have 2D array and I don't want to go 
> vertical. Something like :
>
> int[3][3] matrix = [
>     [ 1, 2, 3 ],
>     [ 4, 5, 6 ],
>     [ 7, 8, 9 ]
> ];
>
> I believe I can use std.range function "RoundRobin"(or maybe it 
> won't work with 2D array directly) for having a good looking 
> vertical slice which will have 1,4,7 or 2,5,8 or 3,6,9 in my 
> example above.
>
> And what if I want to go diagonal like 1,5,9 or 3,5,7 in the 
> example above. Is there a good solution in std without using 
> for loops?
>
> I have one more requirement for fulfilling the task that I 
> working on. This slices do not have to be the same size as the 
> array. For example in the example above slice size could have 2 
> instead of 3. In this case I need to have slices like 
> 1,5;2,6;4,8;5,9 ... and so on for diagonal case.
>
> Erdem
>
> Ps: Converting the 2D array to 1D array is possible in my case.

Hello Erdem,

You may want to use mir-algorithm DUB package. It is a D tensor 
library.
https://github.com/libmir/mir-algorithm

import mir.ndslice;

auto slice = matrix[0].ptr.sliced(3, 3);
auto row = matrix[0];
auto col = matrix[0 .. $, 0];

A lot of examples with diagonal and sub-diagonals can be found 
here
http://docs.algorithm.dlang.io/latest/mir_ndslice_topology.html#.diagonal

Best,
Ilya