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(100, 100, 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)