I have data that looks like the following:
df<-tibble( date= seq.Date(as.Date("2021-01-01"), as.Date("2022-02-01"), by = "month"), val1 = c(105, 105, 105, 125, 125, 125, 125, 132, 132, 132, 135, 150, 150, 150), val2 = c(100, 100, 100, 125, 125, 125, 125, 125, 125, 125, 125, 150, 150, 150), diff = val1-val2 )

I am trying to produce the following:
output<-tibble( date= seq.Date(as.Date("2021-01-01"), as.Date("2022-02-01"), by = "month"), val1 = c(105, 105, 105, 125, 125, 125, 125, 132, 132, 132, 135, 150, 150, 150), val2 = c(100, 100, 100, 125, 125, 125, 125, 125, 125, 125, 125, 150, 150, 150), diff = val1-val2, diff_calc = c(0, 0, 0, 5, 5, 5, 5, 5, 5, 5, 5, 22, 22, 22) )

Where diff_calc is the cumulative sum of the previous unique values in diff, where the summing occurs starting where diff = 0 for the previous diff value, and is replicated until diff is 0, and the previous unique diff values are again cumulatively summed.

I have tried different combinations of lags and joins, but am really struggling here. Thanks!