Yes, type in:
?by

for example:
data <- data.frame(fac=factor(c("A","A","B","B")), vec=c(1:4) )
by(data$vec,data$fac, FUN=sum)

Best,
Mikołaj Hnatiuk

2012/11/29 Noah Silverman <noahsilverman@ucla.edu>

> Hi,
>
> I have a very large data set (aprox. 100,000 rows.)
>
> The data comes from around 10,000 "groups" with about 10 entered per group.
>
> The values are in one column, the group ID is an integer in the second
> column.
>
> I want to normalize the values by group:
>
> for(g in unique(groups){
>         x[group==g] / sum(x[group==g])
> }
>
> This works find in a loop, but is slow.  Is there a faster way to do this?
>
> Thanks!
> ______________________________________________
> 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.
>

	[[alternative HTML version deleted]]


