[R] averaging rows on a data.frame according to a factor

David Winsemius dwinsemius at comcast.net
Sat Nov 23 00:01:10 CET 2013

On Nov 22, 2013, at 1:43 PM, john d wrote:

> Dear all,
> I apologize for the newbie question, but I'm stuck.
> I have a data frame in the following form:
> dat<-as.data.frame(cbind(c("a","a","a","b","b"), c(1,2,3,3,2),c(4,3,5,4,4)))
> I need a way to generate a new dataframe with the average for each factor.
> The result should look like:

Well, using the data,frame(cbind(...)) will ensure that you will NOT get factors, since cbind creates a matrix and that structure will not hold factors.

> res<-as.data.frame(cbind(c("a","b"), c(2,2.5),c(4,4)))


Look at ?tapply or ?aggregate.


dat<-data.frame(facts= c("a","a","a","b","b"), nums1=c(1,2,3,3,2),nums2=c(4,3,5,4,4))

aggregate(dat[-1], dat[1], mean)

> Any help would be greatly appreciated.
> Jonathan
> 	[[alternative HTML version deleted]]

Newbie or not, you should still read the Posting Guide.

> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html


David Winsemius
Alameda, CA, USA

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