title: Numpy slicing multiple dimensions by lists
body: <p>Given a matrix, say</p>
  <pre><code>&gt;&gt;&gt; a=np.arange(25).reshape(5,-1)
  </code></pre>
  <p>Can I achieve</p>
  <pre><code>&gt;&gt;&gt; idx=[1,3]
  &gt;&gt;&gt; a[idx][:,idx]
  array([[ 6,  8],
         [16, 18]])
  </code></pre>
  <p>without having to slice <em>a</em> twice?</p>