title: Subsetting 2D array based on condition in numpy python
body: <p>I have a numpy 2D array of size 3600 * 7200. I have another array of same shape which I want to use as a mask.</p>
  
  <p>The problem is that when I do something like this:</p>
  
  <pre><code>import numpy as np
  N = 10
  arr_a = np.random.random((N,N))
  arr_b = np.random.random((N,N))
  arr_a[arr_b &gt; 0.0]
  </code></pre>
  
  <p>The resulting array is no longer 2D, it is 1D. How do I get a 2D array in return?</p>