r - Repeat rows of a data.frame N times

Question

I have the following data frame:

data.frame(a = c(1,2,3),b = c(1,2,3))
  a b
1 1 1
2 2 2
3 3 3

I want to repeat the rows n times. For example, here the rows are repeated 3 times:

  a b
1 1 1
2 2 2
3 3 3
4 1 1
5 2 2
6 3 3
7 1 1
8 2 2
9 3 3

Is there an easy function to do this in R? Thanks!

Answer 1

EDIT: updated to a better modern R answer.

You can use replicate(), then rbind the result back together. The rownames are automatically altered to run from 1:nrows.

d <- data.frame(a = c(1,2,3),b = c(1,2,3))
n <- 3
do.call("rbind", replicate(n, d, simplify = FALSE))

A more traditional way is to use indexing, but here the rowname altering is not quite so neat (but more informative):

 d[rep(seq_len(nrow(d)), n), ]

Here are improvements on the above, the first two using purrr functional programming, idiomatic purrr:

purrr::map_dfr(seq_len(3), ~d)

and less idiomatic purrr (identical result, though more awkward):

purrr::map_dfr(seq_len(3), function(x) d)

and finally via indexing rather than list apply using dplyr:

d %>% slice(rep(row_number(), 3))