From: Rick DeNatale <rick.denatale@...>
Date: 2009-07-29T21:51:23+09:00
Subject: Re: previous value in array block

On Wed, Jul 29, 2009 at 8:11 AM, Robert Dober<robert.dober@gmail.com> wrote:
> On Wed, Jul 29, 2009 at 10:50 AM, Xavier Noria<fxn@hashref.com> wrote:
>> each_cons seems natural here:
>>
>> require 'enumerator'
>>
>> a = [1, 3, 3, 2]
>> b = a[0, 1]
>>
>> a.each_cons(2) { |x, y| b << y - x }
> and purely functional
> ( [0] + a ).each_cons( 2 ).map{ |x,y| y -x }

Here's a lisp/scheme inspired approach using inject and with an array
serving as a "cons cell" and first => car and last => cdr:

[1, 3, 3, 2].inject([0, []]) { |memo, elem| [elem, memo.last << (elem
- memo.first)] }.last # => [1, 2, 0, -1]

-- 
Rick DeNatale

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