From: Rick DeNatale <rick.denatale@...>
Date: 2009-10-05T20:58:08+09:00
Subject: Re: Count the number of times an element occurs in an array

On Mon, Oct 5, 2009 at 6:14 AM, David A. Black <dblack@rubypal.com> wrote:
> Hi --
>
> On Mon, 5 Oct 2009, Jim Burgess wrote:
>
>> Hi,
>>
>> I need to count the number of times an element occurs in an array.
>
> *** DISCLAIMER ***
>
> This answer is just for fun, and because sometimes seeing useful
> techniques in strange contexts helps people learn and remember them.
>
> With that in mind... here's a
>
>>> strings = %w{a b a a c b b b c c c d }
>
> => ["a", "b", "a", "a", "c", "b", "b", "b", "c", "c", "c", "d"]
>>>
>>> hash = Hash.new {|h,k| [k, strings.count(k)] }
>
> => {}
>>>
>>> hash.values_at(*strings.uniq)
>
> => [["a", 3], ["b", 4], ["c", 4], ["d", 1]]
>
> It's not really a good way to count array elements, but it's kind of
> an interesting illustration of some hash semantics.

Or, since we don't use a key more than once one could do:

strings = %w{a b a a c b b b c c c d }

not_a_hash = lambda {|k| [k, strings.count(k)] }

strings.uniq.map {|s| not_a_hash[s]}

  => [["a", 3], ["b", 4], ["c", 4], ["d", 1]]




-- 
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale