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

A fairly extensible solution:

# test data:
df1 <- data.frame(id=letters[1:2])
df2 <- data.frame(id=letters[1:2])

Collect your data into a list then rbind all at once:

dfs <- c("df1","df2")
do.call(rbind, Map("[<-", mget(dfs), TRUE, "source", dfs) )

#      id source
#df1.1  a    df1
#df1.2  b    df1
#df2.1  a    df2
#df2.2  b    df2

Also, note in this example that when you rbind using a named list, your rownames reference the source data. This means you can nearly get what you want using just:

dfs <- c("df1","df2")
do.call(rbind, mget(dfs) )

#      id
#df1.1  a
#df1.2  b
#df2.1  a
#df2.2  b