From: Adam Prescott <mentionuse@...>
Date: 2011-01-29T00:43:37+09:00
Subject: Re: Group elements by category

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On Fri, Jan 28, 2011 at 2:44 PM, Anurag Priyam <anurag08priyam@gmail.com>wrote:

> >> foo = [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]
> >> groups = Hash.new{|h, k| h[k] = []}
> >> foo.each{|i| groups[i] << i}
>
> >> groups     => {1=>[1], 2=>[2, 2], 3=>[3, 3, 3], 4=>[4, 4, 4, 4]}
> >> groups[3] => [3, 3, 3]
>

I think Rails provides this method for pre-1.8.7, but for 1.8.7 and higher
you can use group_by:

>> (1..10).group_by { |n| n % 2 }
=> {0=>[2, 4, 6, 8, 10], 1=>[1, 3, 5, 7, 9]}

which is more easily generalised than the quoted code's approach, and easier
to read, certainly. As an exercise, maybe try implementing your own
Enumerable#group_by method; it's good for getting your head around how #each
and mixins work, as well as yielding to blocks.

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