Subtracting a column value which corresponds to a specific value in another column from the every row in that column in R

results %>%
  group_by(Fish_ID) %>%
  mutate(Inst_Diff = Instance- Instance[First_Success==1])

I want to create a Inst_Diff column. Using instance number where the first success equals to 1 then the ‘Inst_Diff’ is equivalent to: (Instance) – (Instance at at first success). I have more than one Fish_ID. I tried to code above but it gives an error. I would appericate your suggestions. Thank you!

>Solution :

An approach using first

library(dplyr)

df %>% 
  mutate(Inst_Diff = Instance - first(Instance[Success == 1]), .by = Fish_ID)
  Fish_ID Instance Success First_Success Inst_Diff
1       1        0       0             0        -2
2       1        1       0             0        -1
3       1        2       1             1         0
4       1        3       0             0         1
5       1        4       1             0         2
6       1        5       0             0         3