title: Tensorflow Dataset API how to order list_files?
body: <p>I am using the Dataset API <code>list_files</code> in order to get  a list of files in a <code>source</code> directory and <code>target</code> directory, something like:</p>
  
  <pre><code>source_path = '/tmp/data/source/*.ext1'
  target_path = '/tmp/data/target/*.ext2'
  source_dataset = tf.data.Dataset.list_files(source_path)
  target_dataset = tf.data.Dataset.list_files(data_path)
  dataset = tf.data.Dataset.zip((source_dataset, target_dataset))
  </code></pre>
  
  <p>Source and target dir contents have same sequential filenames, but different extensions (e.g, source 0001.ext1 &lt;-> target 0001.ext2).</p>
  
  <p>But since list_files is not ordered in anyway, the zipped dataset contains missmatches between the source and the target.</p>
  
  <p>How can I solve this within the new dataset API?</p>