From: Mike Austin <noone@...>
Date: 2006-11-26T09:20:07+09:00
Subject: Re: ruby and list comprehension

Brad Tilley 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]
> 
> I believe this is known as list comprehension in Python. How is this done in
> Ruby?
> 
> Thanks,
> Brad

Because Ruby's select() returns a value, not just a boolean like in Smalltalk, 
you can do the following:

[1,2,3].select { |x| ![2,3,4].include? x }
[2,3,4].select { |x| ![1,2,3].include? x }
[1,2,3].select { |x| [2,3,4].include? x }

You can also use Array operators:

[1,2,3] - [2,3,4]
[2,3,4] - [1,2,3]
[1,2,3] & [2,3,4]


Mike