From: dblack@...
Date: 2002-11-26T12:45:40+09:00
Subject: Re: each_with_index & collect_with_index?

Hi --

On Tue, 26 Nov 2002, Tim Bates wrote:

> Array.each (and others) have an alternative .each_index which passes the index
> to the element instead of the element itself to the block. Is there an easy
> way to pass both the index and the element, eg something like
> Array.each_with_index{ |i, el| ... }

Yes, there is such a method.  Your notation is a bit off, because it
looks like a class method of Array instead of an instance method of
arrays (actually of enumerables), and the element comes first:

  ar.each_with_index {|el,i| ... }

but anyway, it exists.

> Also, an equivalent for these in 'collect' could be useful, eg
> Array.collect_index{ |i| ... } Array.collect_with_index{ |i, el|
> ... }  How about it?

The first one can be done with:

  (0...array.size).map {|i| ... }

though it's not symmetrical as to the wording.

As for the second....  I recently appointed myself President of
Citizens for MWI [map_with_indices], Inc.  (See
<http://www.ruby-talk.org/51619>).  You may join the organization,
free of charge :-)  Anyway, there's been a lot of talk of this at
various points; if you search for map_with_index and map_with_indices
on the ruby-talk archive, you'll see most of it.  Matz has recently
indicated that he doesn't think there's a demand or need for it.  I'm
still trying to keep the dream alive :-)


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav