From: Laza <lazax.com@...>
Date: 2005-12-01T10:07:31+09:00
Subject: Re: Help constructing interesting hash?

Firstly, you can use Array#zip instead of each_with_index:

h = {}
[1,2,3].zip([:a, :b, :c]){|key, value| h[key] = value }

h
=> {1=>:a, 2=>:b, 3=>:c}


Secondly, here is the answer

h = {}
[1, 2, 2].zip([:a, :b, :c]){|key, value|
        h[key] ||= [];    # if key not defined, make it []
        h[key]<<value
}

h
=> {1=>[:a], 2=>[:b, :c]}

You can also combine the two lines in
        (h[key] ||= []) << value