title: How to get the last N rows of a pandas DataFrame?
body: <p>I have pandas dataframe <code>df1</code> and <code>df2</code> (df1 is vanila dataframe, df2 is indexed by 'STK_ID' &amp; 'RPT_Date') :</p>
  
  <pre><code>&gt;&gt;&gt; df1
      STK_ID  RPT_Date  TClose   sales  discount
  0   000568  20060331    3.69   5.975       NaN
  1   000568  20060630    9.14  10.143       NaN
  2   000568  20060930    9.49  13.854       NaN
  3   000568  20061231   15.84  19.262       NaN
  4   000568  20070331   17.00   6.803       NaN
  5   000568  20070630   26.31  12.940       NaN
  6   000568  20070930   39.12  19.977       NaN
  7   000568  20071231   45.94  29.269       NaN
  8   000568  20080331   38.75  12.668       NaN
  9   000568  20080630   30.09  21.102       NaN
  10  000568  20080930   26.00  30.769       NaN
  
  &gt;&gt;&gt; df2
                   TClose   sales  discount  net_sales    cogs
  STK_ID RPT_Date                                             
  000568 20060331    3.69   5.975       NaN      5.975   2.591
         20060630    9.14  10.143       NaN     10.143   4.363
         20060930    9.49  13.854       NaN     13.854   5.901
         20061231   15.84  19.262       NaN     19.262   8.407
         20070331   17.00   6.803       NaN      6.803   2.815
         20070630   26.31  12.940       NaN     12.940   5.418
         20070930   39.12  19.977       NaN     19.977   8.452
         20071231   45.94  29.269       NaN     29.269  12.606
         20080331   38.75  12.668       NaN     12.668   3.958
         20080630   30.09  21.102       NaN     21.102   7.431
  </code></pre>
  
  <p>I can get the last 3 rows of df2 by:</p>
  
  <pre><code>&gt;&gt;&gt; df2.ix[-3:]
                   TClose   sales  discount  net_sales    cogs
  STK_ID RPT_Date                                             
  000568 20071231   45.94  29.269       NaN     29.269  12.606
         20080331   38.75  12.668       NaN     12.668   3.958
         20080630   30.09  21.102       NaN     21.102   7.431
  </code></pre>
  
  <p>while <code>df1.ix[-3:]</code> give all the rows: </p>
  
  <pre><code>&gt;&gt;&gt; df1.ix[-3:]
      STK_ID  RPT_Date  TClose   sales  discount
  0   000568  20060331    3.69   5.975       NaN
  1   000568  20060630    9.14  10.143       NaN
  2   000568  20060930    9.49  13.854       NaN
  3   000568  20061231   15.84  19.262       NaN
  4   000568  20070331   17.00   6.803       NaN
  5   000568  20070630   26.31  12.940       NaN
  6   000568  20070930   39.12  19.977       NaN
  7   000568  20071231   45.94  29.269       NaN
  8   000568  20080331   38.75  12.668       NaN
  9   000568  20080630   30.09  21.102       NaN
  10  000568  20080930   26.00  30.769       NaN
  </code></pre>
  
  <p>Why ? How to get the last 3 rows of <code>df1</code> (dataframe without index) ?
  Pandas 0.10.1</p>