From: "yermej@..." <yermej@...>
Date: 2007-07-11T22:19:56+09:00
Subject: Re: Repacking an array of arrays

On Jul 9, 10:00 pm, Kaps Lok <jocub...@gmail.com> wrote:
> Is there an elegant (maybe a one-liner) for repacking:
>
> [[1, 4, 7, 10, 13], [2, 5, 8, 11, 14], [3, 6, 9, 12, 15]]
>
> to?
>
> [[1, 4, 7], [10, 13, 2], [5, 8, 11], [14, 3, 6], [9, 12, 15]]
>
> So rather than having 3 arrays each with 5 elements, I get five arrays
> of 3 elements each...
>
> the only way I can see to do this is by looping the array, and creating
> new arrays.
>
> Any help would be much appreciated.

Is the fact that it goes from 3 of 5 to 5 of 3 significant or do you
always want to go to some number of 3 element arrays? E.g. would you
ever have an array of 4 arrays of 6 elements and want to go to an
array of 6 arrays with 4 elements each?

If it's the first case, this will work, though there may be something
more elegant:

result = []
a.flatten.each_with_index {|x, i| i % 3 == 0 ? result << [x] :
result[-1] << x}

I suppose, if you need the second case, you could do something a
little more general:

result = []
a.flatten.each_with_index {|x, i| i % a.length == 0 ? result << [x] :
result[-1] << x}

Jeremy