[R] sorting a data.frame by mean values of grouped data

[Mark W Kimpel]

Stephen,

I am sure someone will have a more elegant solution, but the following 
works. Mark

d.lst <- split(x = d, f = as.factor(d$Group), drop = FALSE)
d.lst.mn <- sapply(d.lst, FUN = 
function(x){mean(as.numeric(as.character(x$Value)))})
o <- order(d.lst.mn, decreasing = TRUE)
d.lst.mn <- d.lst.mn[o]

e <- NULL
for (i in 1:length(d.lst.mn)){
   if (i == 1){
     e <- d[d$Group == names(d.lst.mn)[i],]
   } else {
     e <- rbind(e, d[as.character(d$Group) == names(d.lst.mn)[i],])
   }
}
e

Mark W. Kimpel MD  ** Neuroinformatics ** Dept. of Psychiatry
Indiana University School of Medicine

15032 Hunter Court, Westfield, IN  46074

(317) 490-5129 Work, & Mobile & VoiceMail
(317) 204-4202 Home (no voice mail please)

mwkimpel<at>gmail<dot>com

******************************************************************


sjbarry wrote:
> Hi,
> 
> I have what I think is a fairly straightforward problem. I've looked 
> through the FAQ's and mailing lists but have been unable to identify a 
> solution, probably because I don't understand the language well enough.
> 
> I have a set of data d, with 3 columns as shown,
> I want to sort the data Group, mean(Value by Label). I know that this 
> can be done for one level, say Label, using factor() but I cannot see 
> how to extend that. I have included the code to create the data.frame 
> below and would greatly appreciate a solution or a link to a similar 
> problem that has already been solved in the mailing list.
>    Value Label Group
>      19   Big     A
>      29   Big     A
>      39   Big     A
>      55 Small     D
>      33 Small     D
>      11 Small     D
>      55 Small     D
>      66 Small     D
>      11 Small     D
>      2   Big     C
>      3   Big     C
>      3   Big     C
>      3   Big     C
>      3   Big     C
>      3   Big     C
>      3   Big     C
>      3 Small     B
>      2 Small     B
>      5 Small     B
>      6 Small     B
>      5 Small     B
>      6 Small     B
> 
> Value <- c(19,29,39,55,33,11,55,66,11,2,3,3,3,3,3,3,3,2,5,6,5,6)
> Group <- c("A","A","A","D","D","D","D","D","D",
>     "C","C","C","C","C","C","C","B","B","B","B","B","B")
> Label <- c("Big","Big","Big",
>     "Small","Small","Small","Small","Small","Small",
>     "Big","Big","Big","Big","Big","Big","Big",
>     "Small","Small","Small","Small","Small","Small")
> d <- as.data.frame(cbind(Value, Label, Group))
> 
> 
> Thanks
> 
> Stephen Barry
>