title: Tensorflow Contrib Metrics always return 0.0
body: <p>I tried to use the contrib metrics for the first time and didn't manage to make them work.</p>
  
  <p>Here is the metrics I tried to use, and how they were implemented:</p>
  
  <pre><code>y_pred_labels = y[:, 1]
  y_true_labels = tf.cast(y_[:, 1], tf.int32)
  
  with tf.name_scope('auc'):    
      auc_score, update_op_auc = tf.contrib.metrics.streaming_auc(
          predictions=y_pred_labels, 
          labels=y_true_labels
      )
      tf.summary.scalar('auc', auc_score)
  
  with tf.name_scope('accuracy_contrib'):  
      accuracy_contrib, update_op_acc = tf.contrib.metrics.streaming_accuracy(
          predictions=y_pred_labels, 
          labels=y_true_labels
      )
      tf.summary.scalar('accuracy_contrib', accuracy_contrib)
  
  with tf.name_scope('error_contrib'):
      error_contrib, update_op_error = tf.contrib.metrics.streaming_mean_absolute_error(
          predictions=y_pred_labels, 
          labels=y_[:, 1] ## Needs to use float32 and not int32
      )
      tf.summary.scalar('error_contrib', error_contrib)
  </code></pre>
  
  <p>This code perfectly execute and during execution I obtain the following:</p>
  
  <pre><code>########################################
  Accuracy at step 1000: 0.633333 # This is computed by another displayed not displayed above
  Accuracy Contrib at step 1000: (0.0, 0.0)
  AUC Score at step 1000: (0.0, 0.0)
  Error Contrib at step 1000: (0.0, 0.0)
  ########################################
  </code></pre>
  
  <p>Here is the format of the data inputed:</p>
  
  <pre><code>y_pred_labels = [0.1, 0.5, 0.6, 0.8, 0.9, 0.1, ...] #Represent a binary probability
  y_true_labels = [1, 0, 1, 1, 1, 0, 0, ...] # Represent the true class {0 or 1}
  y_[:, 1]      = [1.0, 0.0, 1.0, 1.0, 1.0, 0.0, 0.0, ...] # Same as y_true_labels formated as float32
  </code></pre>
  
  <p>I think I've understood in the <a href="https://www.tensorflow.org/versions/r1.1/api_docs/python/tf/contrib/metrics/streaming_accuracy" rel="nofollow noreferrer">official documentation</a> that it is normal behavior under certain conditions ... However, I don't manage to obtain the values of my metric.</p>
  
  <hr>
  
  <p>Secondly, I have noticed two of the metrics are called: <strong>streaming_accuracy</strong> and <strong>streaming_auc</strong>, how does it behave differently than in a "<em>non streaming</em>" accuracy or auc metric? And is there any way to make it "non streaming" if necessary ?</p>