From: James Cunningham <jameshcunningham@...>
Date: 2006-11-27T22:00:06+09:00
Subject: Re: ruby and list comprehension

On 2006-11-27 03:30:58 -0500, Robert Klemme <shortcutter@googlemail.com> said:

> 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

That's fair enough, but I think list comprehension is clearer than 
method chaining and one-liner array accumulation. I'm afraid

a << x**2 if x % 2 == 1; a

is perhaps just a little less elegant than

x**2 if x % 2 == 1

I think the nicest thing about Ruby, though, is that it's even possible.

Best,
James