title: Pandas: Exponential smoothing function for column
body: <p>I have the following DataFrame with trading data:</p>
  
  <pre><code>df = pd.DataFrame({
  'Trader': 'Carl Mark Carl Joe Mark Carl Max Max'.split(),
  'Quantity': [5,2,5,10,1,5,2,1],
  'Date' : [
  DT.datetime(2013,1,1,13,0),
  DT.datetime(2013,1,1,13,5),
  DT.datetime(2013,2,5,20,0),
  DT.datetime(2013,2,6,10,0),
  DT.datetime(2013,2,8,12,0),                                      
  DT.datetime(2013,3,7,14,0),
  DT.datetime(2013,6,4,14,0),
  DT.datetime(2013,7,4,14,0),
  ]})
  
  df.index = [df.Date, df.Trader]
  </code></pre>
  
  <p>I hope to compute weekly statistics for each trader with the average order volumes. To do so I am currently unstacking the trader column and resample the data using:</p>
  
  <pre><code>df.unstack('Trader').resample('1W', how='mean').fillna(0)
  </code></pre>
  
  <p>Is there any possibility to compte also a column for each trader with a trend function for the trading volume (preferably a exponential smoothing function based on the previous trades of the trader) ?</p>
  
  <p>Thanks</p>
  
  <p>Andy</p>