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POWhat is the ruby idiomatic way to set a hash entry to a array before appending to it?
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copied!<p>I am trying to create a hash that has a key and an array of values associated with the key. So I was doing something like this</p> <pre><code> hash = Hash.new </code></pre> <p>and then later when I have a key I would do this</p> <pre><code> hash[key] << new_thing </code></pre> <p>but this fails if hash[key] is nil , so I added this statement before trying to append the new_thing to the array.</p> <pre><code> hash[key] = Array.new unless hash[key] hash[key] << new_thing </code></pre> <p>I thought I could eliminate the added statement by changing the definition of hash to</p> <pre><code>hash = Hash.new Array.new </code></pre> <p>but this does not work because each entry shares the same array, what I really need is this</p> <pre><code>hash = Hash.new { |h,k| h[k] = Array.new } </code></pre> <p>I know I am probably splitting hairs but, I am just curious, what would be the "ruby" way to do this?</p> <p><strong>EDIT:</strong> Ultimately what I ended up doing is using group_by. I realize it was not obvious from my question that I was trying to use this structure to group objects with the same property together in a hash. I am including this to encourage others that may find themselves using a similar structure for a similar purpose to check out <a href="http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-group_by" rel="nofollow">group_by</a></p> <pre><code>["A", 1, "b", 3].group_by { |i| i.class } => {String=>["A", "b"], Fixnum=>[1, 3]} </code></pre>

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