title: Expand 1D Numpy array into 2D array of groups of 3
body: <p>Original</p>
  <pre><code>a = np.arange(1, 10)
  </code></pre>
  <p>Expected output</p>
  <pre><code>b = array([[ 1,  2,  3],
     [ 2,  3,  4],
     [ 3,  4,  5],
     [ 4,  5,  6],
     [ 5,  6,  7],
     [ 6,  7,  8],
     [ 7,  8,  9],
     [ 8,  9, 10]])
  </code></pre>
  <p>I can achieve this using</p>
  <pre><code>b = np.array([a[i:i+3] for i in range(10-3)])
  </code></pre>
  <p>but I was wondering if anyone knew a numpy vectorized function to avoid the list comprehension and conversion to array</p>