[R] summing values by group

[Dimitris Rizopoulos]

you could use '?by()', e.g.,

dat <- data.frame(CAT=sample(letters[1:5], 100, TRUE), x=rnorm(100), 
y=rnorm(100), z=rnorm(100))
by(dat[sapply(dat, is.numeric)], dat$CAT, sum)
by(dat[sapply(dat, is.numeric)], dat$CAT, mean)


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: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat/
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Larry White" <ljw1001 at gmail.com>
To: <R-help at stat.math.ethz.ch>
Sent: Thursday, March 24, 2005 5:12 PM
Subject: [R] summing values by group


> At the risk of being wacked for asking what should be obvious....
>
> I have a data frame with one categorical variable "CAT" and several
> numeric variables.  I want to be able to get simple statistics on 
> the
> numeric variables by level.  For example, just as you can use table
> (CAT) to get the counts, I'd like to be able to get the means and 
> sums
> by category.
>
> If someone could point me in the right direction, I'd appreciate it.
> I've been through the SimpleR and Using R for Data Analysis... docs
> and I'm still clueless.
>
> thanks for your help.
>
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