CODEWITHSUNDEEP
rdplyrcumulative-sum
Lief Esbenshade
Lief Esbenshade

Reputation: 833

Cumulative sum with conditional subtraction using dplyr

I am trying to calculate a conditional cumulative sum using the dplyr package in R. I am building a savings calculator with negative shocks. So I want a variable that has cumulative savings, minus the shocks. This seems like it should be fairly straightforward using the lag function, but I can't seem to get it to work.

Here is an example:

event <- c(0,0,0,1,0) 
save <- rep(.5,5)
## add up the savings from each prior row, then when event is one subtract 1
output_want <- c(.5,1,1.5,1,1.5) 
df <- tibble(event,save,output_want) %>% 
  mutate(totsave = if_else(row_number() ==1, save, 0)) %>% 
  mutate(totsave = if_else(row_number() !=1, save+lag(totsave)-event, save))

Ideally I would like to make the negative savings shock be a fraction of the accumulated savings, but thought I'd start with a simpler case.

Upvotes: 1

Views: 712

Answers (1)

josliber
josliber

Reputation: 44320

If at each time step you want to add the savings from the save vector but subtract the shock from event, then you can compute the desired result by taking the cumulative sum of save-event:

cumsum(save-event)
# [1] 0.5 1.0 1.5 1.0 1.5

Upvotes: 2

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