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)) 

Answer 2

For data.frame objects, this solution is several times faster than @mdsummer's and @wojciech-sobala's.

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

For data.table objects, @mdsummer's is a bit faster than applying the above after converting to data.frame. For large n this might flip. .

Full code:

packages <- c("data.table", "ggplot2", "RUnit", "microbenchmark") lapply(packages, require, character.only=T)  Repeat1 <- function(d, n) {   return(do.call("rbind", replicate(n, d, simplify = FALSE))) }  Repeat2 <- function(d, n) {   return(Reduce(rbind, list(d)[rep(1L, times=n)])) }  Repeat3 <- function(d, n) {   if ("data.table" %in% class(d)) return(d[rep(seq_len(nrow(d)), n)])   return(d[rep(seq_len(nrow(d)), n), ]) }  Repeat3.dt.convert <- function(d, n) {   if ("data.table" %in% class(d)) d <- as.data.frame(d)   return(d[rep(seq_len(nrow(d)), n), ]) }  # Try with data.frames mtcars1 <- Repeat1(mtcars, 3) mtcars2 <- Repeat2(mtcars, 3) mtcars3 <- Repeat3(mtcars, 3)  checkEquals(mtcars1, mtcars2) #  Only difference is row.names having ".k" suffix instead of "k" from 1 & 2 checkEquals(mtcars1, mtcars3)  # Works with data.tables too mtcars.dt <- data.table(mtcars) mtcars.dt1 <- Repeat1(mtcars.dt, 3) mtcars.dt2 <- Repeat2(mtcars.dt, 3) mtcars.dt3 <- Repeat3(mtcars.dt, 3)  # No row.names mismatch since data.tables don't have row.names checkEquals(mtcars.dt1, mtcars.dt2) checkEquals(mtcars.dt1, mtcars.dt3)  # Time test res <- microbenchmark(Repeat1(mtcars, 10),                       Repeat2(mtcars, 10),                       Repeat3(mtcars, 10),                       Repeat1(mtcars.dt, 10),                       Repeat2(mtcars.dt, 10),                       Repeat3(mtcars.dt, 10),                       Repeat3.dt.convert(mtcars.dt, 10)) print(res) ggsave("repeat_microbenchmark.png", autoplot(res))