title: Using np.argsort()[::-1] to sort in descending order with same values
body: <p>For example,
  I have a numpy array like: a = np.array([0.5, 0.1, 0.5)].</p>
  <p>When I use np.argsort(a)[::-1] to sort my array in descending order, it returns:</p>
  <blockquote>
  <p>2, 0, 1</p>
  </blockquote>
  <p>Which is technically correct, as np.argsort(a) would return:</p>
  <blockquote>
  <p>1, 0, 2</p>
  </blockquote>
  <p>and I am just reversing the order.</p>
  <p>However, I want the sort to be in the order as the original array, so I would like the return to be:</p>
  <blockquote>
  <p>0, 2, 1</p>
  </blockquote>
  <p>How do I do that? Is there a better function than np.argsort()?</p>