Issue of generating conditional numbers to a set frequency in R

I am having a issue generating conditional numbers. Repeated frequency of the number is shown in "size". For example, 1 should be repeated 3 times and 2 should be repeated 2 times and so on.
My desired output is shown below but I am unable to achieve this. Can somebody correct me please?

Desired output 

   x1
1   1
2   1
3   1
4   2
5   2
6   3
7   4
8   4
9   5
10  5

data <- data.frame(x1= rep(c(1),each=10))
data    

size <- as.array(c(3,2,1,2,2))

for(i in 1:5) {                          
  x_val <- size[i]
  new <- rep(c(x_val), each=x_val)      
  data[nrow(size[i]) + 1, ] <- new      
}
print(data)


   x1
1   1
2   1
3   1
4   1
5   1
6   1
7   1
8   1
9   1
10  1

>Solution :

We could use rep with times

data.frame(x1 = rep(seq_along(size), size))

-output

  x1
1   1
2   1
3   1
4   2
5   2
6   3
7   4
8   4
9   5
10  5

If we need a for loop

x1 <- c()
for(i in seq_along(size)) x1 <- c(x1, rep(i, each = size[i]))
x1
#[1] 1 1 1 2 2 3 4 4 5 5