Create a variable that identifies the original data.frame after rbind command in R

Question

I am relatively new to R and I would like to know how can I create a variable (number sequence) that identifies the each of the original data.frames before being joined with

Answer 1

You can use

transform(dat, newCol = cumsum(ID == 1))

where dat is the name of your data frame and ID is the name of the ID column.