Hi all,

This seems like something that should be possible: how do I grow multidimensional arrays?

I want something like this:

struct X{ ... };
X*[][] listOfLists;
foreach ( x ; otherListOfX ) {
   if ( newListForArbitraryReason ) {
      listOfLists ~= new X*[];
   }

   listOfLists[$] ~= x;
}

Now, this doesn't compile, because I _have_ to give a size to new X*[](arbitrary_number), and the listOfLists[$] ~= x; line never works (hangs at runtime).

So, how would I go about doing this? My apologies if this is something really obvious.

On 10/08/2012 06:12 AM, KillerSponge wrote:
> Hi all,
>
> This seems like something that should be possible: how do I grow
> multidimensional arrays?
>
> I want something like this:
>
> struct X{ ... };
> X*[][] listOfLists;
> foreach ( x ; otherListOfX ) {
> if ( newListForArbitraryReason ) {
> listOfLists ~= new X*[];
> }
>
> listOfLists[$] ~= x;
> }
>
> Now, this doesn't compile, because I _have_ to give a size to new
> X*[](arbitrary_number), and the listOfLists[$] ~= x; line never works
> (hangs at runtime).
>
> So, how would I go about doing this? My apologies if this is something
> really obvious.

I don't see the need for 'new' nor the use of a pointer, so I will not use them (yet): :)

import std.stdio;

struct X
{
    int i;
}

void main()
{
    X[][] listOfLists;

    auto otherListOfX = [ X(1), X(2), X(3) ];
    auto newListForArbitraryReason = true;

    foreach (x; otherListOfX) {
        if (newListForArbitraryReason) {
            X[] newList = [ x ];
            listOfLists ~= newList;
        }
    }

    writeln(listOfLists);
}

The body of foreach can be shorter:

            listOfLists ~= [ x ];

Also note that

- There is no need for the semicolon at the end of the struct definition.

- $ is not a valid index value. The last element is indexed by $-1.

Ali

-- 
D Programming Language Tutorial: http://ddili.org/ders/d.en/index.html

On Monday, 8 October 2012 at 13:56:00 UTC, Ali Çehreli wrote:
> I don't see the need for 'new' nor the use of a pointer, so I will not use them (yet): :)
>
> import std.stdio;
>
> struct X
> {
>     int i;
> }
>
> void main()
> {
>     X[][] listOfLists;
>
>     auto otherListOfX = [ X(1), X(2), X(3) ];
>     auto newListForArbitraryReason = true;
>
>     foreach (x; otherListOfX) {
>         if (newListForArbitraryReason) {
>             X[] newList = [ x ];
>             listOfLists ~= newList;
>         }
>     }
>
>     writeln(listOfLists);
> }
>
> The body of foreach can be shorter:
>
>             listOfLists ~= [ x ];
>
> Also note that
>
> - There is no need for the semicolon at the end of the struct definition.
>
> - $ is not a valid index value. The last element is indexed by $-1.
>
> Ali

Ah, that works great (even with pointers ;)! Thanks a lot! :) It seems so obvious now.

And the use of $ was indeed a stupid mistake on my part. I guess I was confused because of the way it is often used in slicing. I really should pay attention to that :)