title: Sum two columns of a numpy array and add it as a third column of the array
body: <p>I have following numpy array </p>
  
  <p><code>X = np.random.random_integers(100000000,size=(100000000,2))</code></p>
  
  <p>now I want to dd both the columns of the array to generate the third column of the array. I am trying <code>X[3] = X[0]+X[1]</code> but its shape is <code>(2,)</code>. </p>
  
  <p>Example final array :</p>
  
  <pre><code>10    5    15
  15    6    21
  </code></pre>