From: Logan Capaldo <logancapaldo@...>
Date: 2006-10-03T23:11:49+09:00
Subject: Re: sparse multi-dimensional arrays

On Tue, Oct 03, 2006 at 10:58:22PM +0900, Bill Birkett wrote:
> I did like to convert some programs I wrote in Perl to Ruby. I'm 
> working with sparse three dimensional data. Here's an example in 
> Perl. The array @a has just two elements. The rest are undefined.
> 
> #!/usr/bin/perl -w
> 
> $a[0][0][0] = 0;
> $a[100][100][100] = 100;
> 
> print "$a[0][0][0]\n";
> print "$a[100][100][100]\n";
> 
> The output:
> 
> 0
> 100
> 
> Is there an easy way to implement this sort of data  structure in 
> Ruby? The Array class seems limited to one dimension. I looked at the 
> Matrix class, but there doesn't appear to be any way of assigning 
> values to the individual matrix elements (which seems pretty strange, 
> so maybe I'm overlooking the obvious).
> 
It's pretty easy if you know the dimensions before hand, a bit more
hackery pokery if you don't.
a = Array.new(101) { Array.new(101) { Array.new(101) } }
a[0][0][0] = 0
a[100][100][100] = 100

puts a[0][0][0]
puts a[100][100][100]