title: Slicing numpy array taking every nth element
body: <p>I have an numpy array of shape <em>24576x25</em> and i want to extract 3 array out of it. Where the first array contains the every <code>1st,4th,7th,10th,...</code> element
  while second array contains <code>2nd,5,8,11th,...</code> element and third array with <code>3rd,6,9,12th,...</code>
  The output array sizes would be <em>8192x25</em>.
  I was doing the following in <strong>MATLAB</strong></p>
  <pre><code>c = reshape(a,1,[]);
  x = c(:,1:3:end);
  y = c(:,2:3:end);
  z = c(:,3:3:end);
  </code></pre>
  <p>I have tried <code>a[:,0::3]</code> in <strong>python</strong> but this works only if i have array of shape divisible by 3. What can i do?</p>
  <pre><code>X,Y = np.mgrid[0:24576:1, 0:25:1]
  a = X[:,::,3]
  b = X[:,1::3]
  c = X[:,2::3]
  </code></pre>
  <p>does not work either. I need a,b,c.shape = <em>8192x25</em></p>