[R] Mean: category wise within a data frame

[arun]

HI,
May be this helps:


Please use ?dput() to show the example dataset
dat1 <- read.table(text="Categories  Variable Frequencies
1 0.009 1003
1 0.867 1200
1 0.567 987
1 0.765 134
1 0.445 890 
2 0.007 899               
2 0.768 707    
2 0.789 865     
2 0.544  678            
2  0.987 889",sep="",header=TRUE)
library(plyr)
res <-  ddply(transform(dat1,NewCol=Variable*Frequencies),.(Categories),summarize, Avg=mean(NewCol/sum(Frequencies)))


A.K.




On Tuesday, December 24, 2013 10:43 AM, Nandini Jayakumar <nandini_dec6 at hotmail.com> wrote:
Hello all

I have a table a sample of which is as follows:




    
    
    
    



    
    
    
    
        
            Categories

        
        
            Variable (x)

        
        
            Frequencies

        
    
    
        
            1

            1

            1

            1

            1

        
        
            0.009

            0.867

            0.567

            0.765

            0.445

        
        
            1003

            1200

            987

            134

            890

        
    
    
        
            2

            2

            2

            2

            2

        
        
            0.007

            0.768

            0.789

            0.544

            0.987

        
        
            899

            707

            865

            678

            889

        
    
    
        
            3

            3

            3

            3

            3

        
        
            0.898

            0.887

            0.560

            0.098

            0.987

        
        
            544

            677

            934

            467

            876

        
    
    
        
            40

            40

            40

            40

            40

        
        
            0.786

            0.342

            0.456

            0.987

            0.123

        
        
            843

            987

            675

            467

            223

        
    



Basically I have 40 categories and each category has several hundred variables. I want to calculate the average per category, that is variable * frequency/Summation of frequencies. I want to do it for each category separately. Since i have many categories i do not want to use the subset() function 40 times. Is it possible to do it within a single data frame?

Really appreciate any help. Thank you.
                          
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