Collapsing n-dimensional array to linear (1 dimensional)

[NX via Digitalmars-d-learn]

On Friday, 22 January 2016 at 12:07:11 UTC, abad wrote:
> Let's say I have an array like this:
>
> int[][][] array;
>
> And I want to generate a linear int[] based on its data. Is 
> there a standard library method for achieving this, or must I 
> iterate over the array manually?
>
> What I'm thinking of is something like this:
>
> int[] onedim = std.array.collapse(array);

It's not the thing you want but I would suggest using one 
dimensional array like N dimensional array like this:

	int d1 = 10, d2 = 10, d3 = 10;
	int[] arr = new int[d1 * d2 * d3];
	for(int i = 0; i < d1; i++)
		for(int j = 0; j < d2; j++)
			for(int k = 0; k < d3; k++)
				write(arr[(i * d1 * d2) + (j * d2) + (k)]);

This will lead to cache friendly code in most cases as you ensure 
data is packed. It's elements can be iterated with a single 
foreach loop and easier to use in some (many?) cases like when 
using functions that works with one dimensional array.

And if you seriously need multi dimensional array then it's too 
easier to do it yourself:

	int[][][] a = new int[][][](d1, d2, d3);
	int[] collapsed = new int[d1 * d2 * d3];
	foreach(i, q; a)
		foreach(j, w; q)
			foreach(k, e; w)
				collapsed[(i * d1 * d2) + (j * d2) + (k)] = e;