Subset all levels of a single factor

Question

Is there a way to subset all levels of a single factor in one clean swoop?

Case: Assuming you have a data frame where one of the columns is a factor (data$factor) and you want to create subset data frames that contain only one level of the factor. This is simple to do when there are a small number of factors by writing separate subset commands. However, what if you have a large number of levels (e.g. 50+ levels)? Is there a command or a clever way to create all the subsets in such a case without having to write 50+ subset commands?

Answer 1

Without having to create a loop, the SPLIT function is key to solving this problem.

Assuming the factor column you want to subset (or subgroup) is in the column "factor" of the data frame "data" do:

subsets<-split(data, data$factor, drop=TRUE)

This will create a list of subsets based on the factor value. The list will have the same length as the number of factors.

If you need to put each subset in a separate data frame, you can access them by doing the following:

group1<-subsets[[1]]
group2<-subsets[[2]]
...