Conditional cumsum with reset

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I think this is not easily vectorizable…. at least i do not know how.

You can do it by hand via:

my_cumsum <- function(x){
  grp = integer(length(x))
  grp[1] = 1
  for(i in 2:length(x)){
    if(x[i-1] + x[i] <= 10){
      grp[i] = grp[i-1]
      x[i] = x[i-1] + x[i]
    } else {
      grp[i] = grp[i-1] + 1
    }
  }
  data.frame(grp, x)
}

For your data this gives:

> my_cumsum(df$value)
   grp  x
1    1  4
2    1  9
3    2  7
4    2 10
5    3  8
6    3  9
7    4  2
8    4  7
9    4 10
10   5  6
11   5  8
12   6  6
13   6  9
14   6 10
15   7  4

Also for my “counter-example” this gives:

> my_cumsum(c(10,6,4))
  grp  x
1   1 10
2   2  6
3   2 10

As @Khashaa pointed out this can be implementet more efficiently via Rcpp. He linked to this answer How to speed up or vectorize a for loop? which i find very useful

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