title: Ruby: Split / Sort array based on condition
body: <p>I have an array of holidays:</p>
  
  <pre><code>Holiday.all                        
  Holiday Load (0.7ms)  SELECT "holidays".* FROM "holidays"
  =&gt; #&lt;ActiveRecord::Relation [#&lt;Holiday id: 1, name: "Dia da Confraternização Universal", holidayable_id: 1, holidayable_type: "Country", date: "2014-01-01", created_at: "2014-11-05 21:38:13", updated_at: "2014-11-05 21:38:13", verified?: false&gt;, #&lt;Holiday id: 2, name: "Natal", holidayable_id: 1, holidayable_type: "Country", date: "2014-12-25", created_at: "2014-11-05 22:02:33", updated_at: "2014-11-05 22:02:33", verified?: false&gt;]&gt; 
  </code></pre>
  
  <p>I'd like to split this big array of dates by it's dates months, so I'd end up with 12 arrays (one for each month).</p>