[R] summing values by group

Ignacio Colonna
Thu, 24 Mar 2005 18:00:21 -0000

Maybe aggregate() is what you are looking for?

e.g. say your data frame is called 'mydata'

sum.by.CAT<-aggregate(mydata,list(CAT),sum)

this will give you sums by CAT for all the variables in the data set and
will yield 'NA' for any character variables you may have.

Ignacio


-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Larry White
Sent: Thursday, March 24, 2005 10:12 AM
To: R-help at stat.math.ethz.ch
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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