title: How to convert an numpy array of string array to nested numpy array?
body: <p>I have a numpy array of the format: <code>test = array(['[[1,2,3],[2,3,4]]', '[[2,3,4],[4,5,6]]'], dtype='&lt;U17')</code>. I would like to convert it to numpy array of shape <code>(2,2,3)</code>.
  Expected outcome is:</p>
  <pre><code>array([[[1, 2, 3],
          [2, 3, 4]],
         
          [[2, 3, 4],
          [4, 5, 6]]])
  </code></pre>
  <p>Currently, I achieve this by doing - <code>np.array(list(map(lambda x: json.loads(x),test)))</code>.
  I wonder if there's a better way to do this. Any pointers please?</p>