[R] recode Variable in dependence of values of two other variables

[Mikhail Titov]

?aggregate

aggregate(X~ID, your.data.frame.goes.here, "mean")

Mikhail


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
> Behalf Of Julia Moeller
> Sent: Friday, August 12, 2011 10:10 AM
> To: r-help at r-project.org
> Subject: [R] recode Variable in dependence of values of two other
variables
> 
> Hi,
> 
> as an R-beginner, I have a recoding problem and hope you can help me:
> 
> I am working on a SPSS dataset, which I loaded into R (load("C:/...)
> 
> I have  2 existing Variables: "ID" and "X" , and one variable to be
> computed: meanX.dependID (=mean of X for all rows in which ID has the same
> value)
> 
> ID = subject ID.  Since it is a longitudinal dataset, there are repeated
> measurement points for each subject, each of which appears in a new row.
> So, each ID value appears in many rows. (e.g. ID ==1 in row 1:5; ID ==2 in
> rows 6:8 etc).
> 
> 
> Now: For all rows, in which ID has a certain value, meanX.dependID shall
be
> the mean of X in for these rows. How can I automatisize that, without
> having to specify the number of the rows each time?
> 
> e.g.
> 
> 
> ID    X    meanX.dependID
> 1    2    2.25
> 1    3    2.25
> 1    1    2.25
> 1    3    2.25
> 2    5    3.3
> 2    2    3.3
> 2    3    3.3
> 3    4    3
> 3    1    3
> 3    2    3
> 3    3    3
> 3    4    3
> 3    5    3
> 
> 
> Thanks a lot! Hope this is the right place to post, if not, please tell
me!
> best,
> Julia