Question

I have a data frame that looks like this:

a<-c('a', 'b', 'c', 'd', 'e')

b<-c(1, 2, 3, 2, 3)

df<-data.frame(a, b)

      a b
    1 a 1
    2 b 2
    3 c 3
    4 d 2
    5 e 3

I would like to duplicate the values in column a by the number in column b, so as to get a vector/data.frame that looks like this:

c<-c('a', 'b', 'b', 'c', 'c', 'c', 'd', 'd', 'e', 'e', 'e')

       c
    1  a
    2  b
    3  b
    4  c
    5  c
    6  c
    7  d
    8  d
    9  e
    10 e
    11 e

Thanks for your suggestions.

Answer 1

Look at ?rep, as in:

> with(df, rep(a, times = b))
 [1] a b b c c c d d e e e
Levels: a b c d e

The factor bit is annoying as it is how R created b in df. Either do

> df <- data.frame(a, b, stringsAsFactors = FALSE)
> with(df, rep(a, times = b))
 [1] "a" "b" "b" "c" "c" "c" "d" "d" "e" "e" "e"

then the above answer, or just coerce the result to a character vector:

> with(df, as.character(rep(a, times = b)))
 [1] "a" "b" "b" "c" "c" "c" "d" "d" "e" "e" "e"