Repeat rows of a data.frame

Question

I want to repeat the rows of a data.frame, each N times. The result should be a new data.frame (with nrow(new.df) == nrow(old.df) * N) keeping the data types of the columns.

Example for N = 2:

                        A B   C
  A B   C             1 j i 100
1 j i 100     -->     2 j i 100
2 K P 101             3 K P 101
                      4 K P 101

So, each row is repeated 2 times and characters remain characters, factors remain factors, numerics remain numerics, ...

My first attempt used apply: apply(old.df, 2, function(co) rep(co, each = N)), but this one transforms my values to characters and I get:

     A   B   C    
[1,] "j" "i" "100"
[2,] "j" "i" "100"
[3,] "K" "P" "101"
[4,] "K" "P" "101"

Answer 1

df <- data.frame(a = 1:2, b = letters[1:2]) 
df[rep(seq_len(nrow(df)), each = 2), ]