From: "David A. Black" <dblack@...>
Date: 2002-12-03T23:59:40+09:00
Subject: Re: Conditional block operations

Hi --

On Tue, 3 Dec 2002, Roman Rytov wrote:

> Anotehr question is about COLLECT;
>
> myarray.collect {|x| x + ", "}
>
> I wanna execute only over specific emelents (let's say only odd ones or
> all but last).
>
> I know how to do both of them in a couple of lines but RUBY impresses my
> by its brevity. Will it do it in this case too?


You need to get your shift key fixed :-)  There's no RUBY, just Ruby
and ruby.

As for collect'ing selectively, if the elements you *don't* want
are at a known distance from either end of the array, you can do:

  myarray[0..-2].collect {...}  # up to 2nd-to-last element

etc.

Otherwise I think you have to do some kind of pre-filtering.  If we had
map_with_indices, you could do:

  myarray.map_with_indices {|e,i| e + ", " if i % 2 == 0} .compact

but we don't.  (Hint, hint.)

However, you could do:

  (0...myarray.size).map {|i| myarray[i] + ", " if i % 2 == 0} .compact

That's one-line-ish, anyway :-)


David

--
David Alan Black
exiled to ISP shell account due to recalcitrant ISP :-(