title: Manually calculate AUC
body: <p>How can I obtain the AUC value having fpr and tpr? Fpr and tpr are just 2 floats obtained from these formulas:</p>
  
  <pre><code>my_fpr = fp / (fp + tn)
  my_tpr = tp / (tp + fn)
  my_roc_auc = auc(my_fpr, my_tpr)
  </code></pre>
  
  <p>I know this can't pe possible, because fpr and tpr are just some floats and they need to be arrays, but I can't figure it out how to do that so. I also know that I can compute AUC this way:</p>
  
  <pre><code>y_predict_proba = model.predict_proba(X_test)
  probabilities = np.array(y_predict_proba)[:, 1]
  fpr, tpr, _ = roc_curve(y_test, probabilities)
  roc_auc = auc(fpr, tpr)
  </code></pre>
  
  <p>but I want to avoid using predict_proba for some reasons. So my question is: how can I obtain AUC having <code>fp, tp, fn, tn, fpr, tpr</code>? In other words, is it possible to obtain AUC without <code>roc_curve</code>?</p>