On Apr 7, 2010, at 11:41 AM, Peter Ehlers wrote:
On 2010-04-07 8:37, Dimitri Liakhovitski wrote:
Dear R-ers!
# I have a data frame with one factor and 2 numeric variables:
x<-data.frame(group=c("b","b","d","d","e","e"),a=c(1,NA,
10,20,100,200),b=c(5,15,20,NA,10,30))
x
# I want to divide each value of each variable by its group mean -
using plyr and ddply. It works fine, for example, for variable "a":
library(plyr)
x2<-ddply(x, "group", transform, a = a / mean(a, na.rm = T))
x2
# Because I want to do the same for both variables (a and b) I want
to
put it into a function.
# So, I am parametrising the grouping variable and the variable to
transform.
# However, my code below is not working - I know that x[[variable]]
is
not correct - but what is the right way of doing it?
grouping.factor<-"group"
variable<-"a"
x2<-ddply(x, grouping.factor, transform, x[[variable]] =
x[[variable]]
/ mean(x[[variable]], na.rm = T))
Or is there a more effective way of using ddply on a bunch of
variables?
Thank you very much for your advise!
Yes, there is: colwise()
f <- function(x) x / mean(x, na.rm = TRUE)
ddply(x, "group", colwise(f, c("a", "b")))
Which might also be productive strategy for yesterday's question (for
which we have yet to be offered reproducible data example, however):
https://stat.ethz.ch/pipermail/r-help/2010-April/234363.html
--
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
