title: Numpy, how to reshape a vector to multi column array
body: <p>I am wondering how to use np.reshape to reshape a long vector into n columns array without giving the row numbers.</p>
  
  <p>Normally I can find out the row number by <code>len(a)//n</code>:</p>
  
  <pre><code>a = np.arange(0, 10)
  n = 2
  b = a.reshape(len(a)//n,n)
  </code></pre>
  
  <p>If there a more direct way without using <code>len(a)//n</code>?</p>