iterative cumsum where sum determines the next position to be added

Question

I have a data.table as follows

set.seed(5)
x <- data.table(x=sample(1:20,15))

> x
     x
 1:  5
 2: 14
 3: 17
 4: 20
 5:  2
 6: 11
 7:  8
 8: 15
 9: 12
10         


        

Answer 1

A base R solution:

i = 1
v = i
sum = 0
while (i <= nrow(x)) {
   v = c(v, i)
   sum = sum + x$x[i]
   i = sum
}