Repeat rows of a data.frame
There is a lovely vectorized solution that repeats only certain rows n-times each, possible for example by adding an ntimes
column to your data frame:
A B C ntimes
1 j i 100 2
2 K P 101 4
3 Z Z 102 1
Method:
df <- data.frame(A=c("j","K","Z"), B=c("i","P","Z"), C=c(100,101,102), ntimes=c(2,4,1))
df <- as.data.frame(lapply(df, rep, df$ntimes))
Result:
A B C ntimes
1 Z Z 102 1
2 j i 100 2
3 j i 100 2
4 K P 101 4
5 K P 101 4
6 K P 101 4
7 K P 101 4
This is very similar to Josh O'Brien and Mark Miller's method:
df[rep(seq_len(nrow(df)), df$ntimes),]
However, that method appears quite a bit slower:
df <- data.frame(A=c("j","K","Z"), B=c("i","P","Z"), C=c(100,101,102), ntimes=c(2000,3000,4000))
microbenchmark::microbenchmark(
df[rep(seq_len(nrow(df)), df$ntimes),],
as.data.frame(lapply(df, rep, df$ntimes)),
times = 10
)
Result:
Unit: microseconds
expr min lq mean median uq max neval
df[rep(seq_len(nrow(df)), df$ntimes), ] 3563.113 3586.873 3683.7790 3613.702 3657.063 4326.757 10
as.data.frame(lapply(df, rep, df$ntimes)) 625.552 654.638 676.4067 668.094 681.929 799.893 10
df <- data.frame(a = 1:2, b = letters[1:2])
df[rep(seq_len(nrow(df)), each = 2), ]
A clean dplyr
solution, taken from here
library(dplyr)
df <- tibble(x = 1:2, y = c("a", "b"))
df %>% slice(rep(1:n(), each = 2))