title: Numpy (or scipy) frequency count along columns in 2D array
body: <p>I have a 2D array like so</p>
  
  <pre><code>array([[ 1,  0, -1],
         [ 1,  1,  0],
         [-1,  0,  1],
         [ 0,  1,  0]])
  </code></pre>
  
  <p>I'd like to get the max frequency value along each column. For the above matrix, I'd like to get [1, 0, 0] (or [1,1,0], since both 0 and 1 occur twice in the second column).</p>
  
  <p>I've looked into numpy.unique, but it only takes 1D arrays. bincount won't work since I have negative numbers in my array. I also need a vectorized implementation (since I have thousands of rows in the matrix).</p>