title: Getting index of first occurrence in each row
body: <p>I have this array full of Boolean values:</p>
  
  <pre><code>array([[[ True,  True, False, False, False, False],
          [ True, False, False, False, False, False]],
  
         [[False, False, True, False, True, False],
          [ True, False, False, False, False, False]],
  
         [[ True, False, False, False, False, False],
          [ True, False, False, False, False, False]]], dtype=bool)
  </code></pre>
  
  <p>I want to get indexes of first occurrences of True in each column in each row so the answer would be something like that:</p>
  
  <pre><code>array([[0,0,0],
        [0,1,0],
        [1,0,2],
        [1,1,0],
        [2,0,0],
        [2,1,0]])
  </code></pre>
  
  <p>Is there a simple and fast way of doing so?</p>