title: A fast way to find the largest N elements in an numpy array
body: <p>I know I  can do it like the following:</p>
  
  <pre><code>import numpy as np
  N=10
  a=np.arange(1,100,1)
  np.argsort()[-N:]
  </code></pre>
  
  <p>However, it is very slow since it did a full sort.</p>
  
  <p>I wonder whether numpy provide some methods the do it fast.</p>