title: Converting Pandas Dataframe to numpy array
body: <p>The following is a Pandas dataframe <code>df</code></p>
  
  <pre><code>index_column      value_column
   0                   20
   2                   28
   1                   30
  </code></pre>
  
  <p>It needs to be converted into a numpy array where <code>index_column</code> becomes the index of numpy array and <code>value_column</code> becomes the corresponding value.</p>
  
  <p>That is <code>np_arr[0]=20</code>, <code>np_arr[1]=30</code>, <code>np_arr[2]=28</code> and so on.</p>
  
  <p>How can this be achieved?</p>