keep same values?

[River Huang]

Dear all, I found this question here (http://bbs.pinggu.org/thread-6752140-1-1.html). The data is:

* Example generated by -dataex-. To install: ssc install dataex
clear
input float(id x)
1 3
1 4
1 5
1 6
2 3
2 4
2 7
2 8
end

There are only two groups for `id' (1 or 2). For `id=2', I'd like to keep the observations where the values of `x' of `id=2' appear in the values of `x' of `id=1'. The desired result is

* Example generated by -dataex-. To install: ssc install dataex
clear
input float(id x)
1 3
1 4
1 5
1 6
2 3
2 4
end

Any suggestions?

[Clyde Schechter]

* Example generated by -dataex-. To install: ssc install dataex
clear
input float(id x)
1 3
1 4
1 5
1 6
2 3
2 4
2 7
2 8
end


by x (id), sort: drop if id == 2 & _N == 1
sort id x

list, noobs sepby(id)

Hat tip @Romalpa Akzo.

[River Huang]

Dear Clyde, Thanks a lot for this interesting suggestion.