From: Jason Nordwick <jason@...>
Date: 2006-10-04T02:17:46+09:00
Subject: Re: sparse multi-dimensional arrays

Close:

a={}
a[[0,0,0]], a[[100,100,100]] = 0, 100
puts "#{a[[0,0,0]]}"
puts "#{a[[100,100,100]]}"

But you might like this better (my Ruby isn't very good, so please excuse me if I overcomplicate these definitions):

class SparseMatrix < Hash
 alias :oldget :[]
 alias :oldset :[]=
 def[](*i); self.oldget(i); end
 def[]=(*i); v=i.pop; self.oldset(i,v); end
end

a = SparseMatrix.new
a[0,0,0], a[100,100,100] = 0, 100


irb(main):017:0> a
=> {[0, 0, 0]=>0, [100, 100, 100]=>100}
irb(main):018:0> puts "#{a[0,0,0]}"
0
=> nil
irb(main):019:0> puts "#{a[100,100,100]}"
100
=> nil
irb(main):020:0> puts "#{a[2,2,2]}"

=> nil
irb(main):021:0>

-j


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).
> 
> -Bill