st: Collapse & Missing Values

["Eric G. Wruck" <ewruck@econalytics.com>]

I just learned, rather inconveniently, that collapse doesn't work the 
way I'd like when encountering missing values.  Here's an example:
. l

     +----------------------+
     |        date   amount |
     |----------------------|
  1. | 10-Oct-1990      200 |
  2. | 10-Oct-1990      -75 |
  3. | 10-Oct-1990       64 |
  4. | 11-Oct-1990        . |
  5. | 12-Oct-1990      107 |
     |----------------------|
  6. | 12-Oct-1990        . |
     +----------------------+

. collapse (sum) net_amt=amount, by(date)

. l

     +-----------------------+
     |        date   net_amt |
     |-----------------------|
  1. | 10-Oct-1990       189 |
  2. | 11-Oct-1990         0 |
  3. | 12-Oct-1990       107 |
     +-----------------------+

.
The problem is for the single 11-Oct-1990 observation.  After 
collapsing, the missing value becomes a zero; in this instance I 
would have preferred it remain missing.  The 12-Oct-1990 treatment is 
fine & what I expected.  I suppose I could delete observations before 
performing the collapse but it would be better if there was some 
other option.  Is there?


Grazie,


Eric

--

===================================================

       Eric G. Wruck
       Econalytics
       2535 Sherwood Road
       Columbus, OH  43209

       ph:      614.231.5034
       cell:    614.330.8846
       eFax:    614.573.6639
       eMail:   ewruck@econalytics.com
       website: http://www.econalytics.com

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