title: TypeError: cannot concatenate a non-NDFrame object
body: <p>I have this DatetimeIndex:</p>
  
  <pre><code>dates = DatetimeIndex(['2017-06-09', '2017-06-10', '2017-06-11', '2017-06-12',
                 '2017-06-13', '2017-06-14'],
                dtype='datetime64[ns]', freq='&lt;DateOffset&gt;')
  </code></pre>
  
  <p>I want to take dates and append them to my DataFrame <code>df</code>:</p>
  
  <pre><code>for i in xrange(0,5):
      df.append(dates[i],ignore_index=True)
  </code></pre>
  
  <p>I get this error <code>TypeError: cannot concatenate a non-NDFrame object</code>.</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>sample data of <code>df</code>:</p>
  
  <pre><code>Out[85]:
  2017-06-05   -0.944868
  2017-06-06    0.073623
  2017-06-07   -0.687232
  Freq: &lt;DateOffset&gt;, dtype: float64
  </code></pre>