title: Dataframe to Influxdb -- ValueError: The truth value of a DataFrame is ambiguous
body: <p>I'm trying to write a simple dataframe into influx and this are my columns:</p>
  <p><strong>Index</strong>     ////       <strong>Tag 1</strong>      ////      <strong>Field 1</strong>    ////     <strong>Field 2</strong></p>
  <p>I have checked various documentation, tried a number of &quot;solutions&quot; but I continue to get errors.</p>
  <pre><code>data_frame['index'] = pd.to_datetime(data_frame['index'])
  data_frame = data_frame.set_index('index')
  client.write_points(data_frame, 'measurement', tags = { 'ID': data_frame[['ID']] })
  </code></pre>
  <p>I get the following error:
  ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().</p>
  <p>Does anyone know what is wrong?</p>