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

[sjbarry]

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

-- 

School of Earth and Environmental Sciences
University of Wollongong
Northfields Ave.
Wollongong, NSW. 2522
Australia