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averaging rows on a data.frame according to a factor

5 messages · john d, David Winsemius, Rui Barradas +1 more

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

            

      
      
      
    

        
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.

            

      
      
      
    

        
Ouch.


Look at ?tapply or ?aggregate.

Perhaps:

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)

            

      
      
      
    

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

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Rui Barradas
    

    

      
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Hello,

Try the following.

aggregate(cbind(V2, V3) ~ V1, dat, FUN = mean)


Hope this helps,

Rui Barradas

Em 22-11-2013 21:43, john d escreveu:

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Rui Barradas
    

    

      
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Sorry, there's a bug in my previous answer.

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

aggregate(as.matrix(dat[,-1]) ~ dat[,1], FUN = mean)


Don't use as.data.frame(cbind(...)), everything becomes factors.

Rui Barradas

Em 22-11-2013 23:02, Rui Barradas escreveu:

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      arun
    

    

      
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Hi,


dat<-as.data.frame(cbind(c("a","a","a","b","b"), c(1,2,3,3,2),c(4,3,5,4,4)))
?str(dat)
#'data.frame':??? 5 obs. of? 3 variables:
# $ V1: Factor w/ 2 levels "a","b": 1 1 1 2 2
# $ V2: Factor w/ 3 levels "1","2","3": 1 2 3 3 2
# $ V3: Factor w/ 3 levels "3","4","5": 2 1 3 2 2

#better way would be
dat<-data.frame(V1=c("a","a","a","b","b"), V2=c(1,2,3,3,2),V3=c(4,3,5,4,4))
?str(dat)
#'data.frame':??? 5 obs. of? 3 variables:
# $ V1: Factor w/ 2 levels "a","b": 1 1 1 2 2
# $ V2: num? 1 2 3 3 2
# $ V3: num? 4 3 5 4 4

library(plyr)
?ddply(dat,.(V1),colwise(mean))

#or
?aggregate(.~V1,data=dat,mean)

A.K.

        
On Friday, November 22, 2013 5:45 PM, john d <dobzhanski at gmail.com> 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:

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

Any help would be greatly appreciated.

Jonathan

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