st: create a variable based on a recurring value in a varlist

[Derek Darves <darves@uoregon.edu>]

Hi all,

I have a group of variables:

PID1 - PID15

PID* takes on values from 1 to 8000, and many are missing.

Basically, I would like to make a new variable, called interlock,  
that is equal to 1 if any of the variables in the list are equal to  
any other variable in the list (not including itself, of course).
For example, if PID5==705 and PID14==705 I would like like interlock==1

Likewise, if none of the the variables in PID* take on the value of  
any of the other variables in PID*, I would like interlock==0

I tried this:
egen interlock = group(pid1_a  pid1_b  pid2_a  pid2_b  pid3_a   
pid3_b  pid4_a pid4_b  pid5_a  pid5_b  pid6_a  pid6_b  pid7_a   
pid7_b  pid8_a  pid8_b  pid9_a  pid9_b  pid10_a  pid10_b  pid11_a   
pid11_b  pid12_a  pid12_b  pid13_a  pid13_b  pid14_a  pid14_b   pid15_a)

, but it returned all missing values when I know that some share a  
common value in two of the PID* fields.

Lastly, not that it should matter, but the above is a simplifying  
example. In my actual dataset I have about 130 PID* variables. I just  
mention this in case I am hitting some kind of memory limitation (I  
am not receiving any errors when I run the command, though, it just  
doesn't work).

Thanks in advance,

Derek

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