From: Rob Biedenharn <Rob@...>
Date: 2007-12-15T00:44:49+09:00
Subject: Re: each with previous?

On Dec 14, 2007, at 10:28 AM, Jari Williamsson wrote:

> I'm going through lots of data where the result of the current is  
> affected by the previous element. So what I would need is an
> "each_with_previous {|current, prev|}"
> ...to make it a bit more readable. Is there any built-in Ruby method  
> that I might have overlooked, or should I build my own?
>
> Best regards,
>
> Jari Williamsson


require 'enumerator'


[first, second, third].each_slice(2) do |prev,curr|
   # do stuff
end

Except that you don't get a [nil,first] pair to start, you get  
[first,second].

You could also do something like:

[first, second, third].inject(nil) do |prev, curr|
   # do stuff
   curr
end

And curr is assigned to prev in the next iteration and the first  
iteration gets [nil,first]

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com