I have this dataframe with 5 column where stock is the current_stock. And i want a new column stock_over_time which is then calculated as stock_over_time = stock - sales + purchase.
df=tibble(article=rep("article one",5),
week=c(1,2,3,4,5),
sales=10,
purchase=c(5,0,5,5,0),
stock=c(50))
# A tibble: 5 x 5
article week sales purchase stock
<chr> <dbl> <dbl> <dbl> <dbl>
1 article one 1 10 5 50
2 article one 2 10 0 50
3 article one 3 10 5 50
4 article one 4 10 5 50
5 article one 5 10 0 50
My final dataframe should look like this:
# A tibble: 5 x 5
article week sales purchase stock stock_over_time
<chr> <dbl> <dbl> <dbl> <dbl> <dbl>
1 article one 1 10 5 50 NA
2 article one 2 10 0 50 45
3 article one 3 10 5 50 35
4 article one 4 10 5 50 30
5 article one 5 10 0 50 25
...where stock_over_time is calculated as:
50 - 10 + 5 = 45
45 - 10 + 0 = 35
35 - 10 + 5 = 30
30 - 10 + 5 = 25
How would i do this?