Merging issue with using data since the variables cannot uniquely identify observations

[Tariq Abdullah]

Hello, This is my master data. My master is repeated cross section.

* Example generated by -dataex-. For more info, type help dataex
clear
input float year double county
2001 10093
2001 10093
2001 10003
2001 10003
2002 10093
2002 10093
2002 10003
2002 10003
2002 10003
2002 10001
2003 10001
2003 10001
2003 10003
2003 10003
end

This is my using data. My plan is to have a panel using data but the error message something else which I'll post after posting the sample using data below.

* Example generated by -dataex-. For more info, type help dataex
clear
input float(year county)
2000  1003
2000  1097
2000  1129
2000  6001
2000  6005
2000  6009
2000  6013
2000  6041
2000  6055
2000  6059
2000  6067
2000  6077
2000  6081
2000  6085
2000  6087
2000  6095
2000  6099
2002 10001
2002 10003
2002 11001
2002 12003
2002 12007
2002 12011
2002 12015
2002 12019
end

So when I'm merging master with the using data by the following command

 merge m:1 year county using "trade.dta", keep(master match) nogen

I get this error message

 merge m:1 year county using "trade.dta", keep(master match) nogen
(variable year was int, now float to accommodate using data's
       values)
(variable county1 was float, now double to accommodate using
       data's values)
variables year county do not uniquely identify observations in
    the using data
r(459);

end of do-file

r(459);

The issue is when I'm using the dataex command I don't see any repeated observation based on -dataex year county- command. But, after using the xtset and isid command I get the following information for my using data:

 isid year county
variables year and county should never be missing
r(459);

xtset year county

Panel variable: year (unbalanced)
 Time variable: county, 1003 to 55133, but with gaps
         Delta: 1 unit

May you kindly what problem in using data is causing the merging problem issue with the master data? Because the error clearly says while merging variables year county do not uniquely identify observations in
the using data

[Tariq Abdullah]

In my using data I had some observations for which the value of county was missing. Therefore , I was having the problem. After fixing that merging was successful with master data.

[Clyde Schechter]

Thank you for closing the thread by posting the solution you arrived at. Future readers will benefit from that.

[Tariq Abdullah]

Happy to do so ! This is the least I could do given that how gracious statalist community has been to me over time