From: Robert Dober <robert.dober@...>
Date: 2007-05-09T17:18:43+09:00
Subject: Re: Implementation of the object.sort method.

On 5/9/07, Jorge Domenico Bucaran Romano <jbucaran@gmail.com> wrote:
> Hi,
>
> Can you show me an implementation of the Array.sort method? This
> implementation would be demonstrative only. This would handle when a
> block is passed. The reason is I have trouble understanding why the
> following code works as expected:
>
> [3,2,1,4].sort do |a,b|
>     a <=> b
> end
>
> I know it will sort my array but I don't understand the way this method
> works because other tests I have made bring none results.
>
> Regards, Jorge.
>

Actually you do not need to know anything about the implementation.
Ruby uses a modified Quicksort as Phrogz pointed out.
The block is just delivering the operation *every* sorting algorithm
must eventually apply, "comparison".
The result of the block applied to two arbitrary elements of the array
(assigned to the parameters a and b) will determine if the LHS is
smaller, equal or greater than the RHS. (depending on the values <0, 0
or >0 respectively).

If you use the variation #sort_by the block will be applied to both
elements first and the results of these applications are compared than
(using <=> if I am not mistaken ).

If you understand the differnce bewteen
a.sort{ rand } and a.sort_by{ rand }
you have grasped the concept.

HTH
Robert


-- 
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw