From: CBlair1986 <CBlair1986@...>
Date: 2006-11-18T18:15:04+09:00
Subject: Re: Splitting an array into quads and putting them back together again.



On Nov 16, 7:37 am, "Martin DeMello" <martindeme...@gmail.com> wrote:
> On 11/16/06, Chris Blair <cblair1...@gmail.com> wrote:
>
>
>
> > Thanks! I don't quite understand the code, right now, but it does work
> > exactly how I wanted it. Sorry for the delay in responding, I haven't had
> > access to the internet for a little while.Here's a quick explanation of how the code works:
>
> Ruby's multidimensional arrays are actually arrays of arrays. So if you have
>
> a1 = [[1,2],[5,6]]
> b1 = [[3,4],[7,8]]
> a2 = [[9,10],[13,14]]
> b2 = [[11,12],[15,16]]
>
> and you want
>
> a = [[1,2,5,6],  [3,4,7,8], [9,10,13,14], [11,12,15,16]]
>
> you need (i) a way to combine two submatrices side by side and (ii) a
> way to combine them one on top of the other.
>
> Let's start with side by side, defining the | operator so that
>
> [[1, 2],
>  [5, 6]] |
> [[3, 4],
>  [7, 8]] =
>
> [[1, 2, 3, 4],
>  [5, 6, 7, 8]]
>
> To do that we need to walk over each row of both arrays, in parallel,
> and combine the rows into one big row. The #zip method steps over two
> enumerables in parallel, returning pairs of elements, so that
>
> [a, b].zip([c,d]) #=>  [[a, c], [b, d]]
>
> Let's take that for a spin:
> <snip/>
> irb(main):099:0> [a1, b1, a2, b2].shape(2)
> => [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]
>
> and there we are.
>
> martin

Thank you for the in-depth explanation. It really helped me grasp what
you did. Honestly, I would never have thought about the problem as you
did, so I see I've got a lot more to learn. Thank you again!