Return complete multi-dimensional array after appending

[eXodiquas]

On Wednesday, 15 September 2021 at 21:02:29 UTC, Paul Backus 
wrote:
> On Wednesday, 15 September 2021 at 20:32:12 UTC, eXodiquas 
> wrote:
>> ```d
>> [1,0,3,4,0,5]
>> .fold!((a, e) => e != 0 ? a[0] ~ e : a[1] ~ e)(cast(int[][]) 
>> [[],[]])
>> .flatten
>> .writeln
>> ```
>> This should sort all non 0s into the `a[0]` array and all 0s 
>> into the `a[1]` array. But it won't work because the `~` does 
>> not return the whole array (which is probably better for most 
>> of the cases). So the question, is there a way to do this kind 
>> of append, but getting the whole array back as a result in std?
>
> You need to use `~=` instead of `~` to mutate an existing array:
>
> ```d
> import std;
>
> void main()
> {
>     [1, 0, 3, 4, 0, 5]
>         .fold!((a, e) {
>             e != 0 ? (a[0] ~= e) : (a[1] ~= e);
>             return a;
>         })(cast(int[][]) [[], []])
>         .joiner
>         .writeln;
> }
> ```
>
> Of course, a more idiomatic solution would be to use 
> `std.algorithm.partition`:
>
> ```d
> import std;
>
> void main()
> {
>     auto arr = [1, 0, 3, 4, 0, 5];
>     arr.partition!(e => e != 0); // in-place
>     arr.writeln;
> }
> ```

Oooh, I totally forgot you can open blocks like this in anonymous 
functions. Now I look a bit stupid. Thanks. :) `partition` is 
also very nice. D std is so huge, I should sketch out a roadmap 
or something. That's why I asked the question in the first place 
because deep inside I knew there is a function in std that solves 
the problem.

Thanks for the answer. :)