[R] intersect of 2 data frames

Dimitris Rizopoulos Dimitris.Rizopoulos at med.kuleuven.be
Sun May 6 21:33:51 CEST 2007

look at ?merge(), e.g., try something like the following:

merge(pretestm, posttest, by = "StuNum")

check also the on-line help page for more info, especially for the  
'all' argument.

I hope it helps.


Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/

Quoting Salvatore Enrico Indiogine <hindiogine at gmail.com>:

> Greetings!
> I am a new user of R.  The only one in my department, all others use SPSS.
> I have two data sets of students with test scores, pretest and
> posttest.  The first column StuNum and then columns of scores.
> The problem is that the lists are slightly different not all students
> are in both data sets.
> So I did:
> intersect(pretest$StuNum, posttest$StuNum) -> common.id
> At this point I need to select from pretest the students in common.id
> and do the same with posttest.
> I have tried several things but, basically I do not know how to do so.
> In SQL it should be something like:
> select pretest$StuNum in common.id
> Any pointers?
> Thanks,
> Enrico
> --
> Enrico Indiogine
> Mathematics Education
> Texas A&M University
> hindiogine at gmail.com
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