From: dblack@...
Date: 2002-11-09T08:35:19+09:00
Subject: Re: Multi-dimensional (like 2) arrays in Ruby

Hi --

On Sat, 9 Nov 2002, Ted wrote:

> All of the replies say the same thing -- this is good.  My learning
> project for Ruby is implementing a turning grille cipher. I want to
> allocate a n*m matrix where n and m are read from stdin.
>
> I have the n[] (the rows) array, no sweat.  But the m part (the
> columns) is rather elusive.

There's a Matrix class shipped with Ruby -- have a look at
lib/matrix.rb.

> Here's my latest code:
>
> @m = Array.new(@rows)
> @M = @m.each {|row| @m[row] = Array.new(@cols)}
>
> It doesn't work, either... :-(

Don't forget that #each returns the receiver.  In other words, in
this:

  a = [1,2,3].each {|x| x * 20}

a ends up as [1,2,3], not as [20,40,60].  The transformation is
thrown away.

In your example, you're trying to save the transformation explicitly
to the array that's being transformed... but let Ruby do it for you
:-)  For that purpose, you can use #map.  In fact, you can just map a
series of arrays, based on the number of rows, directly into your
matrix:

  m = (0...rows).map {|r| Array.new(cols)}

Another way to do much the same thing is:

  m = []
  rows.times { m << Array.new(cols) }


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav