title: Mask a 3d array with a 2d mask in numpy
body: <p>I have a 3-dimensional array that I want to mask using a 2-dimensional array that has the same dimensions as the two rightmost of the 3-dimensional array. Is there a way to do this without writing the following loop?</p>
  
  <pre><code>import numpy as np
  
  nx = 2
  nt = 4
  
  field3d = np.random.rand(nt, nx, nx)
  field2d = np.random.rand(nx, nx)
  
  field3d_mask = np.zeros(field3d.shape, dtype=bool)
  
  for t in range(nt):
      field3d_mask[t,:,:] = field2d &gt; 0.3
  
  field3d = np.ma.array(field3d, mask=field3d_mask)
  
  print field2d
  print field3d
  </code></pre>