title: final value in column of exponentially weighted average values
body: <p>I have a dataframe stockData which looks like this:</p>
  
  <pre><code>Name:   BBG.XLON.VOD.S_MKTCAP_EUR,
  04/02/2008  125761.8868
  05/02/2008  124513.4973
  06/02/2008  124299.8368
  07/02/2008  122973.7429
  08/02/2008  123451.0086
  11/02/2008  122948.5002
  12/02/2008  124336.3475
  13/02/2008  124546.6607
  14/02/2008  124434.8762
  15/02/2008  123370.2129
  18/02/2008  123246.854
  19/02/2008  121965.328
  20/02/2008  119154.8945
  </code></pre>
  
  <p>I am trying to create an exponentially weighted moving average with an alpha of 0.1, so the resulting dataframe should look like:</p>
  
  <pre><code>Name:   BBG.XLON.VOD.S_MKTCAP_EUR,  expon
  04/02/2008  125761.8868 125761.8868
  05/02/2008  124513.4973 125637.0478
  06/02/2008  124299.8368 125503.3267
  07/02/2008  122973.7429 125250.3683
  08/02/2008  123451.0086 125070.4324
  11/02/2008  122948.5002 124858.2391
  12/02/2008  124336.3475 124806.05
  13/02/2008  124546.6607 124780.111
  14/02/2008  124434.8762 124745.5876
  15/02/2008  123370.2129 124608.0501
  18/02/2008  123246.854  124471.9305
  19/02/2008  121965.328  124221.2702
  20/02/2008  119154.8945 123714.6327
  </code></pre>
  
  <p>I have tried using the following from panadas:</p>
  
  <p>stockData['expon'] = pd.ewma(stockData[unique_id+"_MKTCAP_EUR"], span = 0.1)</p>
  
  <p>but get a result which does not equal what I am expecting:</p>
  
  <pre><code>Name:   BBG.XLON.VOD.S_MKTCAP_EUR,  expon
  04/02/2008  125761.8868 125761.8868
  05/02/2008  124513.4973 123681.2377
  06/02/2008  124299.8368 124062.4362
  07/02/2008  122973.7429 121107.3884
  08/02/2008  123451.0086 124216.9907
  11/02/2008  122948.5002 122075.8313
  12/02/2008  124336.3475 126868.3597
  13/02/2008  124546.6607 124942.6688
  14/02/2008  124434.8762 124220.0306
  15/02/2008  123370.2129 121296.275
  18/02/2008  123246.854  123004.4148
  19/02/2008  121965.328  119431.9075
  20/02/2008  119154.8945 113577.3494
  </code></pre>
  
  <p>Could someone let me know what I need to do in order to return the expected result please.</p>
  
  <p>Also if I wanted just to return the last value in the exponentially weighted series (123714.6327) could someone also let me know how that would be possible please?</p>
  
  <p>Thanks</p>