title: Numpy - How to vectorize on Sub-Arrays
body: <p>How do you apply vectorized functions on sub-arrays? Suppose I have the following:</p>
  
  <pre><code>array = np.array([
      [0, 1, 2],
      [2],
      [],
  ])
  </code></pre>
  
  <p>And I wanted to obtain the first element in each subarray, else <code>None</code>.</p>
  
  <p><code>[0, 2, None]</code></p>
  
  <p>While simple, is there are way to do this leveraging Numpy's pure vectorization? There doesn't seem to be native operations, and the <code>np.vectorize()</code> function is described to not be true documentation and has been stated at various other points in threads.</p>
  
  <p>Is my only option to do a <code>np.apply_along_axes()</code>?</p>
  
  <p>When do I know when I cannot solve my problem with numpy's pure vectorization?</p>