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

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)