title: Add complementary values to numpy array
body: <p>I have a 1D numpy array, for example the following:</p>
  
  <pre><code>import numpy as np
  arr = np.array([0.33, 0.2, 0.8, 0.9])
  </code></pre>
  
  <p>Now I would like to change the array so that also one minus the value is included. That means the array should look like:</p>
  
  <pre><code>[[0.77, 0.33],
   [0.8, 0.2],
   [0.2, 0.8],
   [0.1, 0.9]]
  </code></pre>
  
  <p>How can this be done?</p>