title: How to get unique value in multidimensional array
body: <p>I have done a lot of looking around on the overflow, and on google, but none of the results works for my specific case.</p>
  
  <p>I have a placeholder array called $holder, values as follows:</p>
  
  <pre><code>    Array ( 
      [0] =&gt; Array ( 
          [id] =&gt; 1 
          [pid] =&gt; 121 
          [uuid] =&gt; 1  
          )
      [1] =&gt; Array ( 
          [id] =&gt; 2 
          [pid] =&gt; 13
          [uuid] =&gt; 1
          )
      [2] =&gt; Array ( 
          [id] =&gt; 5 
          [pid] =&gt; 121 
          [uuid] =&gt; 1
          )
      ) 
  </code></pre>
  
  <p>I am trying to pull out distinct/unique values from this multidimensional array.  The end result I would like is either a variable containing (13,121), or (preferrably) an array as follows:
  Array(
      [0] => 13
      [1] => 121
  )</p>
  
  <p>Again I've tried serializing and such, but don't quite understand how that works when operating with a single key in each array.</p>
  
  <p>I tried to be as clear as possible.  I hope it makes sense...</p>