title: How to select specific column indices from a matrix?
body: <p>I have a matrix and a list of column indices that I want to select from the matrix for each row. How can I do that in numpy?</p>
  
  <pre><code>my_matrix = np.array([[1, 2], [4, 5]])
  col_idx = np.array([1, 0])
  selected = .... # selects 1st element of row 0 and 0th element of row 1.
  print selected
  # np.array([2, 4])
  </code></pre>