How can I repeat a data.frame?

Question

It\'s easy to repeat a data.frame once,

mt2 <- rbind(mtcars, mtcars)

But what\'s an R-like way to do this generally? If I want 10 copies

Answer 1

dplyr-based solution (from here)

library(dplyr)
mtcars %>% slice(rep(1:n(), 2))  # 2 copies of data frame

Answer 2

Here's a very simple method:

mtcars[rep(1:nrow(mtcars),2),]

or using better "grammar":

mtcars[rep(seq_len(nrow(mtcars)),2),]

As GSee notes below, one difference here is that rbind will replicate the row names exactly, while using indexing will force unique row names by appending digits. Off the top of my head, I think the only fix would be to set the row names (again using rep) after the fact.

Answer 3

If you can tolerate another package:

require(mefa)
rep(mtcars,10)

• works after all!

It appears a little faster:

system.time(mtcars[rep(1:nrow(mtcars),1e5),])
system.time(mtcars[rep(seq_len(nrow(mtcars)),1e5),])
system.time(rep(mtcars,1e5))

Gives:

 user  system elapsed 
 17.41    0.19   17.89
 17.11    0.31   17.91
 6.79    0.70    7.67

Caveats: 1) rep will not reproduce the row names; this is a separate step. 2) mefa::rep(mtcars,10) doesn't work as: Error: 'rep' is not an exported object from 'namespace:mefa'. Also mefa:::rep(mtcars,10) gives object 'rep' not found. Not sure why this is...

Answer 4

@joran's answer is very elegant and you should use it if duplicating the rownames isn't required. However, this way will also duplicate the rownames:

do.call(rbind, replicate(10, mtcars[1:10, ], simplify=FALSE))