title: can't read one array csv file corrently with tf.decode_csv()
body: <p>I have hundreds of csv files, each of them contains one array, which is the input array of my network.
  I tried to use <code>tf.data.TextLineDataset</code> to generate a dataset of csv file names and use <code>dataset.map()</code> to read them.  However, I get very confused with how to use <code>tf.decode_csv()</code></p>
  
  <p>Say the csv content is</p>
  
  <pre><code>1 2 3 4 5 ... 100
  </code></pre>
  
  <p>Then using:</p>
  
  <pre><code>dataset = tf.data.TextLineDataset(['a.csv','b.csv', ...])
  dataset.map(proc)
  </code></pre>
  
  <p>Where:</p>
  
  <pre><code>def proc(csv):
      array = tf.decode_csv(csv,[0.0 for i in range(1000)])
      return array
  </code></pre>
  
  <p>I get:</p>
  
  <pre><code># array = (tensor, shape=1) * 100
  </code></pre>
  
  <p>If use:</p>
  
  <pre><code>def proc(csv):
      array = tf.decode_csv(csv,[[0.0]])
      return array
  </code></pre>
  
  <p>I get:</p>
  
  <pre><code># array = (tensor, shape=1)
  </code></pre>
  
  <p>This means only one value of the array is read.</p>
  
  <p>How should the array be read into <code>(tensor, shape=100)</code>?</p>