I have a dataset with columns: date, product, sales. I want to calculate the cumulative sum of sales for each product over time.

Here’s a sample of my data:

library(dplyr)

data <- data.frame(
  date = rep(seq(as.Date("2023-01-01"), length.out = 10, by = "day"), 3),
  product = rep(c("A", "B", "C"), each = 10),
  sales = sample(100:200, 30, replace = TRUE)
)

I’ve tried using group_by and cumsum, but I’m getting unexpected results. Any help would be appreciated!

Tried: Used group_by(product) and cumsum(sales).
Expected: Cumulative sum for each product.
Result: Incorrect cumulative sum across all products.