title: Results of custom top K accuracy differ from Keras top_k_categorical_accuracy
body: <p>I am using my own top K accuracy metric for multi label classification:</p>
  
  <pre><code>def top_K_acc(y_true, y_pred, k):
      assert y_true.shape == y_pred.shape
      top_k_indx = np.argsort(y_pred, axis=1)[:,::-1][:,:k]
      n_guessed = 0
      for i in range(len(y_true)):
          if np.any(y_true[i,top_k_indx[i]]):
              n_guessed += 1
      print(n_guessed / len(y_true))
  </code></pre>
  
  <p>but it's always shows higher accuracy than <code>top_k_categorical_accuracy</code> from Keras. What am I doing wrong?</p>