From: Robert Klemme <shortcutter@...>
Date: 2006-11-27T17:35:08+09:00
Subject: Re: ruby and list comprehension

On 27.11.2006 01:01, James Cunningham wrote:
> On 2006-11-26 17:52:37 -0500, dblack@wobblini.net said:
>> I'm not getting how that's better than:
>>
>>    added = new_data.select {|x| not old_data.include?(x) }
>>
>> (or the reject equivalent) and so on.

> I should have clarified. In your example there's no difference, but the 
> above gives a general replacement for list comprehensions.
> 
> irb(main):018:0> (1..25).to_a.comprehend { |x| x**2 if not x % 2 == 0 }
> => [1, 9, 25, 49, 81, 121, 169, 225, 289, 361, 441, 529, 625]

Frankly, I am not sure I find this better than using the built in methods:

irb(main):001:0> (1..25).inject([]) {|a,x| a << x**2 unless x % 2 == 0; a}
=> [1, 9, 25, 49, 81, 121, 169, 225, 289, 361, 441, 529, 625]

irb(main):002:0> (1..25).inject([]) {|a,x| a << x**2 if x % 2 == 1; a}
=> [1, 9, 25, 49, 81, 121, 169, 225, 289, 361, 441, 529, 625]

irb(main):003:0> (1..25).select {|x| x % 2 == 1}.map! {|x| x**2}
=> [1, 9, 25, 49, 81, 121, 169, 225, 289, 361, 441, 529, 625]

Kind regards

	robert