title: concatenate and remove duplicate element from numpy arrays
body: <p>I compute an array of indices in each iteration of a loop and then I want to remove the duplicate elements and concatenate the computed array to the previous one. 
  For example the first iteration gives me this array:</p>
  
  <pre><code>array([  1,   6,  56, 120, 162, 170, 176, 179, 197, 204])
  </code></pre>
  
  <p>and the second one:</p>
  
  <pre><code>array([ 29,  31,  56, 104, 162, 170, 176, 179, 197, 204]) 
  </code></pre>
  
  <p>and so on. How could I do it?</p>