Matched pairs with two data frames

-----Original Message-----
From: r-help-bounces at r-project.org 
[mailto:r-help-bounces at r-project.org] On Behalf Of Udo
Sent: Monday, 14 April 2008 6:41 a.m.
To: r-help at r-project.org
Subject: [R] Matched pairs with two data frames

Hi,
I have a frame "treat" and want to find matched pairs in the 
data frame "control". In the matched (combined) data frame 
there should be two variables (0/1),indicating the "source" 
of the data (treat or control), so that it is possibe to set 
a "filter" (extraxt/select data).

#Here are the dataframes (my real data frames have many 
variables) treat <- data.frame(age=c(1,1,2,2,2,4),
                    school=c(10,10,20,20,20,11),
                    out1=c(9.5,2.3,3.3,4.1,5.9,4.6)) control 
<- data.frame(age=c(1,1,1,1,3,2),
                      school=c(10,10,10,10,33,20),
                      out2=c(1.1,2,3.5,4.9,5.2,6.5))
print(treat)
print(control)

matched.data.frame <- ?????? #Match "treat" "control" by age school


#My SPSS syntax would be similar to this:
MATCH FILES FILE="treat" /IN=fromtreat
  /FILE="control" /IN=fromcontrol
  /BY age school.
SELECT IF fromdad AND fromfam. #select data, set filter

The /IN= option creates a 0/1 variable that indicates the 
"source" of the data

The resultand matched data frame should have the following structure:
age   school    out1    out2  fromtreat     fromcontrol
1	10	9.5	1.1  	1		1
1	10	2.3	2.0  	1		1
....
4	11	4.6	NA   	1		0
3	33	NA	5.2	0		1
....

I tried "which" and "match", but I failed and was unlucky 
looking at the help/archive. Merge doesn?t do the job, 
because it makes all possible matches.


Thank?s for any help!
Udo


--------------------------------------------
Udo K    N     G
      ?     I

Clinic for Child an Adolescent Psychiatry Philipps University 
of Marburg / Germany