title: Create 2D array from Pandas dataframe
body: <p>Probably a very simple question, but I couldn't come up with a solution. 
  I have a data frame with 9 columns and ~100000 rows. The data was extracted from an image, such that two columns ('row' and 'col') are referring to the pixel position of the data. How can I create a numpy array A such that the row and column points to another data entry in another column, e.g. 'grumpiness'?  </p>
  
  <pre><code>A[row, col]
  #  0.1232
  </code></pre>
  
  <p>I want to avoid a for loop or something similar. </p>