From: Mauricio Fernandez <mfp@...>
Date: 2006-07-05T19:32:30+09:00
Subject: Re: Parallel Array

On Wed, Jul 05, 2006 at 11:36:31AM +0900, Gregory Brown wrote:
> On 7/4/06, Matthew Smillie <M.B.Smillie@sms.ed.ac.uk> wrote:
> 
> ># using inject is fun.  Let's do it again.
> >c = (0...a.length).inject([]) { |x, n| x << a[n] + b[n] }
> 
> better would be c = (0...a.length).inject([]) { |x, n| x + [ a[n] + b[n] ] }

ugh this is doubly slow. #inject, an extra literal array and an Array#+ for
each pair, making it O(n**2)...

If you absolutely want to feel smart for using #inject,

 a = [1,2,3,4]
 b = [1,1,2,2]
 c = a.inject([[],0]){|(arr, i),e| [arr << e+b[i], i + 1]}.first
 c                                                 # => [2, 3, 5, 6]

... but it's still silly. Either use the Array initializer, manual aref in a
a.size.times block, or look into narray.

-- 
Mauricio Fernandez  -   http://eigenclass.org   -  singular Ruby