r - Split dataframe using two columns of data and apply common transformation on list of resulting dataframes

Question

I want to split a large dataframe into a list of dataframes according to the values in two columns. I then want to apply a common data transformation on all dataframes (lag transformation) in the resulting list. I'm aware of the split command but can only get it to work on one column of data at a time.

Answer 1

You need to put all the factors you want to split by in a list, eg:

split(mtcars,list(mtcars$cyl,mtcars$gear))

Then you can use lapply on this to do what else you want to do.

If you want to avoid having zero row dataframes in the results, there is a drop parameter whose default is the opposite of the drop parameter in the "[" function.

split(mtcars,list(mtcars$cyl,mtcars$gear), drop=TRUE)