It is relatively easy to collapse data in R using one or more BY variables and a defined function.
# aggregate data frame mtcars by cyl and vs, returning means # for numeric variables attach(mtcars) aggdata <-aggregate(mtcars, by=list(cyl,vs), FUN=mean, na.rm=TRUE) print(aggdata) detach(mtcars)
When using the aggregate() function, the by variables must be in a list (even if there is only one). The function can be built-in or user provided.
To practice aggregate() and other functions, try the exercises in this manipulating data tutorial.