How to generate a sequential character vector without a loop?

Question

I'm trying to generate a character vector that includes a sequence of n numbers (as character) with m empty string elements in between each number element.

I managed to generate the vector using a loop. Is there a way to implement this more conciseley without a loop, and would this be more efficient?

sequence = character(0)
n = 3
m = 2

for(i in 1:n){
  sequence <- c(sequence, rep("",m), i)
  i <- i + 1
}

The output is a vector like:

c("","","1","","","2","","","3")

Answer 1

Here is another way to with rep and lapply.

seq_fun <- function(n, m){
  unlist(lapply(1:n, function(x) c(rep("", times = m), x)))
}

seq_fun(3, 2)
# [1] ""  ""  "1" ""  ""  "2" ""  ""  "3"

Answer 2

1) Create an m by n matrix of "" and rbind 1:n to the bottom of it. Then unravel that into a vector:

c(rbind(matrix("", m, n), 1:n))
## [1] ""  ""  "1" ""  ""  "2" ""  ""  "3"

2) Another approach is to create an m1*n long vector of "" and replace positions m1*(1:n) with 1:n.

m1 <- m + 1
replace(character(m1 * n), m1 * (1:n), 1:n)
## [1] ""  ""  "1" ""  ""  "2" ""  ""  "3"

Alternately we could use a logical second argument:

replace(character(m1 * n), c(logical(m), TRUE), 1:n)
## [1] ""  ""  "1" ""  ""  "2" ""  ""  "3"