title: Scikit.learn auc function TypeError
body: <p>I am following <a href="https://stackoverflow.com/a/31161137/7807920">this StackOverflow answer</a> to compute the AUC score in my data, but if I try to run the script it gives me back a TypeError.</p>
  
  <blockquote>
    <p>TypeError: ufunc 'subtract' did not contain a loop with signature
    matching types dtype('S32') dtype('S32') dtype('S32')</p>
  </blockquote>
  
  <p>I don't understand, because the <code>roc_curve</code> function works fine, so I would expect that the <code>auc</code> function should work too.
  I'have already checked the <code>dtype</code> of my test arrays and they are all <code>float64</code>.</p>
  
  <p>Thanks for your help.</p>