dplyr / R cumulative sum with reset

Question

I\'d like to generate cumulative sums with a reset if the \"current\" sum exceeds some threshold, using dplyr. In the below, I want to cumsum over \'a\'.

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Answer 1

I think you can use accumulate() here to help. And i've also made a wrapper function to use for different thresholds

sum_reset_at <- function(thresh) {
  function(x) {
    accumulate(x, ~if_else(.x>=thresh, .y, .x+.y))
  }  
}

tib %>% mutate(c = sum_reset_at(5)(a))
#       t     a     c
#     
# 1     1     2     2
# 2     2     3     5
# 3     3     1     1
# 4     4     2     3
# 5     5     2     5
# 6     6     3     3
tib %>% mutate(c = sum_reset_at(4)(a))
#       t     a     c
#     
# 1     1     2     2
# 2     2     3     5
# 3     3     1     1
# 4     4     2     3
# 5     5     2     5
# 6     6     3     3
tib %>% mutate(c = sum_reset_at(6)(a))
#       t     a     c
#     
# 1     1     2     2
# 2     2     3     5
# 3     3     1     6
# 4     4     2     2
# 5     5     2     4
# 6     6     3     7