title: Array of strings Group by first common letters
body: <p>Is there anyway of grouping first common letters in an array of strings?</p>
  
  <p>For example:</p>
  
  <pre><code> array = [ 'hello', 'hello you', 'people', 'finally', 'finland' ]
  </code></pre>
  
  <p>so when i  do</p>
  
  <pre><code>array.group_by{ |string| some_logic_with_string }
  </code></pre>
  
  <p>The result should be,</p>
  
  <pre><code>{ 
     'hello' =&gt; ['hello', 'hello you'],
     'people' =&gt; ['people'],
     'fin' =&gt; ['finally', 'finland']
  }
  </code></pre>