From: Louis J Scoras <louis.j.scoras@...>
Date: 2006-11-26T09:06:43+09:00
Subject: Re: ruby and list comprehension

On 11/25/06, Brad Tilley <rtilley@vt.edu> wrote:

> In Python, I can do this to arrays:
>
> added = [x for x in new_data if x not in old_data]
> removed = [x for x in old_data if x not in new_data]
> same = [x for x in new_data if x in old_data]

Short answer:

    added   = new_data.reject {|i| old_data.include? i }
    removed = old_data.reject {|i| new_data.include? i }
    same    = new_data.select {|i| old_data.include? i }

Provided ordering isn't important here, you can do the same thing with
set operations.

    require 'set'

    old_data = old_data.to_set
    new_data = new_data.to_set

    added   = new_data - old_data
    removed = old_data - new_data
    same    = new_data.intersection(old_data)

Note those returns sets, not arrays.


-- 
Lou.