st: Replacing values within a matched study

["Nada Khan" <Nada.Khan@dphpc.ox.ac.uk>]

Hi, 

I'm having trouble putting my finger on the solution to what may be a simple problem. 

I have a matched case control dataset with patients who have had breast, colon or prostate cancer with 4 matched controls each and a matching variable (groupid).  My data looks like this:

id    groupid     breast    colon    prostate  control
1        1              1            .              .             .
2        1              .            .               .             1
3        1              .             .              .             1
4        1              .             .               .            1
.
.
.
89     40             .             1              .             .
90     40            .              .               .             1
91     40            .              .              .              1
etc 

What I'm trying to do is replace breast = 0 for each control, or colon= 0 for each control, so that my data would look like this:

id    groupid     breast    colon    prostate  control
1        1              1            .              .             .
2        1              0            .               .             1
3        1              0             .              .             1
4        1              0            .               .             1
.
.
.
89     40             .             1              .             .
90     40            .              0               .             1
91     40            .              0              .              1
etc 

I can't seem to get the right combination of gen/replace/bys commands.  Can anyone help?

Thanks!
Nada



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