title: Append not working with DataFrames in for loop
body: <p>I have a time series with 3 columns. I need to copy column 2 after the last row and the same with the column 3. </p>
  
  <p>I created a for loop and append the dataframes, but the append doesn't seem to work. There is no error or warning, just doesn't work.</p>
  
  <p>Initial DataFrame dataImport_selVar100:</p>
  
  <pre><code>    val01_ambient_temperature   val01_ambient_winddir   val01_ambient_windspeed
  measure_time            
  2019-03-24 07:30:00 12.956060   108.200005  4.166667
  2019-03-24 07:40:00 12.999207   103.000000  3.666667
  2019-03-24 07:50:00 12.761206   106.500000  4.533333
  2019-03-24 08:00:00 12.523205   98.413330   3.916667
  2019-03-24 08:10:00 12.285204   97.853333   4.055000
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>counterTest=0
  for column in dataImport_selVar100:
      if counterTest==0: #initialize
          result0=pd.DataFrame(dataImport_selVar100.iloc[:,counterTest])
      else:
          result1=pd.DataFrame(dataImport_selVar100.iloc[:,counterTest])
          result0.append(result1,ignore_index=True,sort=False)
  
      #print(result[column])
      counterTest +=1
  </code></pre>
  
  <p>The actual results are just the ones from result0 (100 rows)</p>
  
  <pre><code>&lt;class 'pandas.core.frame.DataFrame'&gt;
  DatetimeIndex: 100 entries, 2019-03-24 07:30:00 to 2019-03-25 00:00:00
  Data columns (total 1 columns):
  val01_ambient_temperature    100 non-null float64
  dtypes: float64(1)
  memory usage: 6.6 KB
  </code></pre>
  
  <p>The expected results are the sum of all the rows </p>
  
  <pre><code>&lt;class 'pandas.core.frame.DataFrame'&gt;
  DatetimeIndex: 300 entries, 2019-03-24 07:30:00 to 2019-03-25 00:00:00
  Data columns (total 3 columns):
  val01_ambient_temperature    100 non-null float64
  val01_ambient_winddir        100 non-null float64
  val01_ambient_windspeed      100 non-null float64
  dtypes: float64(2)
  memory usage: 7.0 KB
  </code></pre>