From: "Kroeger, Simon (ext)" <simon.kroeger.ext@...>
Date: 2006-08-21T23:01:28+09:00
Subject: Re: You can write Fortran in any language

 

> From: Bil Kleb [mailto:Bil.Kleb@NASA.gov] 
> Sent: Monday, August 21, 2006 3:20 PM
> 
> How about the (i,j) beasts?   E.g.,
> 
>    sum_xy = Array.new(x.size){ Array.new(y.size){0.0} }
>    for k in 0..n-1
>      for i in 0...x.size
>        for j in 0...y.size
>          sum_xy[i][j] += x[i][k]*y[j][k]
>        end
>      end
>    end
> 
> Doubly embedded maps?
> 
> Is there anyway to do all this without using indices?

sum_xy = x.map do |i|
  y.map do |j|
    (0..n-1).inject(0) {|sum, k| sum + i[k] * j[k]}
  end
end

to get rid of the last index you would need zip or
SyncEnumerator (which is slow).
 
> Agreed.  I'm happy to locally extend Enumerable...
> 
>    module Enumerable
>      def sum
>        self.inject(0){ |sum,e| sum + e }
>      end
>    end

module Enumerable
 def sum
   inject{|sum, e| sum + e}
 end
end

hmm, at least if the enumerable isn't empty ...

cheers

Simon