st: Collapsing with strings

[Marcello Pagano <pagano@hsph.harvard.edu>]

For Daphna Bassok:

Hi-

I am having a frustrating problem and would love some advice.

I have several duplicate observations in my data set.  However, they are 
not perfect duplicates.  Only the id # is the same. So there might be 
two observations with id#16 for instance, the first will have values for 
some variables, and missing values for others. The second also have some 
values filled and some missing.  There are no cases in which both have 
values- that is... either the first in the pair has the value OR the 
second has a value (or neither).

For example: suppose I have two observations with id# 16...  The first 
has values for var1 and  2 and not 3.   The second ONLY has values for 
var 3.   What i would like to do is simply collapse these into a single 
observation with all the relevant info. meaning, 1 observation with 
id#16 that has values for all three variables.

I am trying to do this with the collapse command with no success.

My code is:

collapse (min) var1-var3, by(id)

I thought this would create a new observation that has all the data in it.

I am getting a "type mismatch" error.

Is this because some of my variables are string variables?

How can i get around this?

Thanks in advance for your help,

daphna
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