title: numpy.where() detailed, step-by-step explanation / examples
body: <p>I have trouble properly understanding <code>numpy.where()</code> despite reading <a href="http://docs.scipy.org/doc/numpy-1.10.1/reference/generated/numpy.where.html" rel="noreferrer">the doc</a>, <a href="https://stackoverflow.com/questions/5642457/how-does-python-numpy-where-work">this post</a> and <a href="https://stackoverflow.com/questions/24219841/numpy-where-on-a-2d-matrix">this other post</a>.</p>
  
  <p>Can someone provide step-by-step commented examples with 1D and 2D arrays?</p>