title: Filling empty python dataframe using loops
body: <p>Lets say I want to create and fill an empty dataframe with values from a loop. </p>
  
  <pre><code>import pandas as pd
  import numpy as np
  
  years = [2013, 2014, 2015]
  dn=pd.DataFrame()
  for year in years:
      df1 = pd.DataFrame({'Incidents': [ 'C', 'B','A'],
                   year: [1, 1, 1 ],
                  }).set_index('Incidents')
      print (df1)
      dn=dn.append(df1, ignore_index = False)
  </code></pre>
  
  <p>The append gives a diagonal matrix even when ignore index is false:</p>
  
  <pre><code>&gt;&gt;&gt; dn
         2013  2014  2015
  Incidents                  
  C             1   NaN   NaN
  B             1   NaN   NaN
  A             1   NaN   NaN
  C           NaN     1   NaN
  B           NaN     1   NaN
  A           NaN     1   NaN
  C           NaN   NaN     1
  B           NaN   NaN     1
  A           NaN   NaN     1
  
  [9 rows x 3 columns]
  </code></pre>
  
  <p>It should look like this:</p>
  
  <pre><code>&gt;&gt;&gt; dn
         2013  2014  2015
  Incidents                  
  C             1   1   1
  B             1   1   1
  A             1   1   1
  
  [3 rows x 3 columns]
  </code></pre>
  
  <p>Is there a better way of doing this? and is there a way to fix the append? </p>
  
  <p>I have pandas version '0.13.1-557-g300610e'</p>