From: Robert Feldt <feldt@...>
Date: 2001-03-16T18:05:14+09:00
Subject: [ruby-talk:12735] Re: Sum of Squares

On Fri, 16 Mar 2001, Luigi Ballabio wrote:

> To follow up on the Haskell-functional programming thing, this is where
> [1,2,3].zip([4,5,6])                # --> [[1,4],[2,5],[3,6]]
> and
> [1,2,3].inject(0) { |a,b| a+b }     # --> 1+2+3 = 6
> could come handy - the above would be
> class Array
>      def dot(other)
>          self.zip(other).map { |a| a[0]*a[1] } .inject(0) { |a,b| a+b }
>      end
> end
> 
A good example of zip usage, indeed. Thanks for posting.

If I remember correctly there was also a thread on how to sum the
inter-element differences which would be

 ary.zip(ary.tail).map {|a,b| a-b} .inject(0) {|d,s| d+s}

(And, yes we know that there are existing ways to do it... It's Turing 
complete remember ;-))

/Robert