st: filling in missing observations in a panel

[Scott Cunningham <scunning@gmail.com>]

I have a county-level dataset like the following, which has missing  
county ID characteristics.

COUNTY ID | COUNTY | YEAR
001                | Lincoln     | 1992
001                | Lincoln     | 1993
.                      | Lincoln     | 1994
001                | Lincoln     | 1995

I need to find all missing observations in the "County ID" column,  
and replace them with the appropriate value.  I know this is simple,  
but have forgotten how.

sc
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