title: pandas resampling without performing statistics
body: <p>I have a five minute dataframe:</p>
  
  <pre><code>rng = pd.date_range('1/1/2011', periods=60, freq='5Min')
  df = pd.DataFrame(np.random.randn(60, 4), index=rng, columns=['A', 'B', 'C', 'D'])
  
                              A         B         C         D
  2011-01-01 00:00:00  1.287045 -0.621473  0.482130  1.886648
  2011-01-01 00:05:00  0.402645 -1.335942 -0.609894 -0.589782
  2011-01-01 00:10:00 -0.311789  0.342995 -0.875089 -0.781499
  2011-01-01 00:15:00  1.970683  0.471876  1.042425 -0.128274
  2011-01-01 00:20:00 -1.900357 -0.718225 -3.168920 -0.355735
  2011-01-01 00:25:00  1.128843 -0.097980  1.130860 -1.045019
  2011-01-01 00:30:00 -0.261523  0.379652 -0.385604 -0.910902
  </code></pre>
  
  <p>I would like to resample only the data on the 15 minute interval, but without aggregating into a statistic (I dont want the mean,median,stdev).I want to subsample and get the actual data on the 15 minute interval.Is there a builtin method to do this?</p>
  
  <p>My output would be:</p>
  
  <pre><code>                            A         B         C         D                 
  2011-01-01 00:00:00  1.287045 -0.621473  0.482130  1.886648                 
  2011-01-01 00:15:00  1.970683  0.471876  1.042425 -0.128274                 
  2011-01-01 00:30:00 -0.261523  0.379652 -0.385604 -0.910902                 
  </code></pre>