[R] generating a new variable based on results of a by command

[Dimitris Rizopoulos]

maybe you want to use ave(), e.g.,

f$sums <- ave(f$b, f$e, FUN = sum)


I hope it helps.

Best,
Dimitris

----
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/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Economics Guy" <economics.guy at gmail.com>
To: <r-help at stat.math.ethz.ch>
Sent: Thursday, June 21, 2007 3:53 PM
Subject: [R] generating a new variable based on results of a by 
command


>I have a matrix with a set of variables one of which is a factor. 
>Using by()
> I have calculated something about each group (say the sum). Now I 
> want to
> create a new variable in the original matrix that contains the 
> results of
> the by() for each observation that is in the corresponding group.
>
> For example I have:
>
> ---------
>
> a <-c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16)
>
> b <-c(7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22)
>
> e 
> <-c("A","B","C","D","E","F","A","B","C","D","E","F","D","E","F","A")
>
> f <-data.frame(e,a,b)
>
> # Calculate sum by group
>
> sums <- by(f, e, function(x) sum(x$b))
>
> -----------
>
> Now I would like to assign each observation in f a new variable 
> based on the
> results of the by(). I converted sums into a matrix and then tried 
> using
> match() and ifthen() but could not get it to work.
>
> Thanks,
>
> EG
>
> [[alternative HTML version deleted]]
>
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