From: Thomas Wieczorek <wieczo.yo@...>
Date: 2008-01-29T22:30:55+09:00
Subject: Re: Proposal/RFQ: Hash#values/keys with block

On Jan 29, 2008 2:10 PM, Dirk Traulsen <dirk.traulsen@lypso.de> wrote:
> hash = { 'a' => 1, 'bb' => 2, 'c' => 33, 'dd' => 44}
>
> hash.keys                           #=> ["a", "bb", "c", "dd"]
> hash.values                         #=> [1, 2, 33, 44]
>
> hash.values {|k,v| k > 'a' }        #=> [2, 33, 44]
>

I am sure you could use external iterators for that and extend your Hash class.
(I'll try it later)

> hash.values {|k,v| v % 2 == 0 }     #=> [2, 44]
>

This one goes easily with a select call:
hash.values.select {|el| el % 2 == 0 }   #=> [2, 44]

> hash.keys {|k,v| k.size == 1 }      #=> ["a", "c"]
>

Same here:
hash.keys.select {|el| el.size == 1 }

> Alternatively they could be implemented as new methods called for
> example
> hash.values_if {}
> hash.keys_if {}
> analogue to the already defined Hash#values_at.
>
> Well, I would prefer the extension of Hash#keys/values with blocks.
> What do you think?
>

I think Array#select does a fine job. You can still write your own
helper methods to implement the behaviour which you need.