title: NumPy hstack throws "ValueError: all the input arrays must have same number of dimensions?"
body: <pre><code>data = [['297348640', 'Y', '12', 'Y'],
         ['300737722','Y', '1', 'Y'],
         ['300074407', 'Y',  '1', 'N']]
  </code></pre>
  
  <p>I want to convert this into a NumPy array so I did:</p>
  
  <pre><code>data = np.array(data)
  </code></pre>
  
  <p>The above is working fine.</p>
  
  <p>Now I have two lists, say</p>
  
  <pre><code>a = [0,2,6]
  b = [21,21,9]
  </code></pre>
  
  <p>I have to append these at last of my previous list:</p>
  
  <pre><code>data = [['297348640', 'Y', '12', 'Y', 0, 21],
         ['300737722','Y', '1', 'Y', 2, 21],
         ['300074407', 'Y',  '1', 'N', 6, 9]]
  </code></pre>
  
  <p>I tried this but its giving me wrong dimension error</p>
  
  <pre><code>a = np.array([a])
  b = np.array([b])
  
  data = np.hstack(data,(a))
  data = np.hstack(data,(b))
  
  ValueError: all the input arrays must have same number of dimensions 
  </code></pre>