From: Saku Ytti <saku@...>
Date: 2008-04-12T15:55:56+09:00
Subject: Re: delete_if, select and (lack of) delete_if!, self.POLS == false

On (2008-04-12 08:27 +0900), ara.t.howard wrote:

>> foo = {}
>> ('a'..'z').each { |l| foo[l] = somearray.select {dosomething} }
>>
> [ 'a', 'a', 'a' ].select{|x| x == 'a'}
>
> and you've clobbered....  not to mention it loses ordering.  the only  
> thing which has semantics inline with that of select is
>
> a.replace a.select(&condition)
>
> which preserves ordering and allows for duplicates.

Yes but if condition needs variable from outer loop (that is, in
my example, you'd use the 'l' from Range object in the 'dosomething'
block, so you're walking through the array multiple times. 
 If you positively know, you want to pick each element exactly once
to a new array/hash. Then having select that reduces the array size
by not forcing you to look at elements you know you're not going
to pick up (as they were already picked up by earlier condition,
to a earlier hash/array, and you know, no future condition can any more
be true for them). If array would be extremely large, the loop
would get the faster the closer to end it is, as array would keep
shrinking.

Thanks,

-- 
  ++ytti