From: Rick DeNatale <rick.denatale@...>
Date: 2007-09-18T22:24:07+09:00
Subject: Re: Is there a select and map for hashes instead of arrays?

With some changes to undo top-posting:
On 9/18/07, James Herdman <james.herdman@gmail.com> wrote:
> On 9/17/07, Jeff <cohen.jeff@gmail.com> wrote:
> > why doesn't Hash#select and Hash#map
> > return hashes instead of arrays?

> My guess is because you need to enumerate over a Hash.  Recall that entries
> in a Hash are indexed by some Hashing algorithm, so it's kind of had to
> enumerate over it's entries.

There's no problem enumerating over a Hash.  Hash#each is implemented
after all.  Enumerable only requires that each yield all of the
elements in SOME order, the fact that Hashes don't have a natural
ordering doesn't hamper this.  Hash#each yields key,value pairs.

Ruby 1.9 is on track to change Hash#select to return a Hash.

Hash#map is problematic though, map returns a new enumeration which
contains the elements resulting in applying the block to each element
yielded by each.  In general this could be anything for example:

    {:a => "fred", :b => "barney"}.map { |k,v| "#{k} is associated
with #{v}"  } # => ["a is associated with fred", "b is associated with
barney"]

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/