R: sum at different levels

Question

I have a dataset X as:

customer_id event_type tot_count
931 1 5
231 2 6
231 1 3
333 3 9
444 1 1
931 3 3
333 1 21
444 2 43

I need a sum at customer_id and event_type level. This is a 1 line code in SQL as:

select customer_id, event_type, sum(tot_count) from X group by 1,2

I need the same operation in R.

Answer 1

You can use the aggregate function:

aggregate(tot_count ~ customer_id + event_type, X, sum)

 customer_id event_type tot_count
1         231          1         3
2         333          1        21
3         444          1         1
4         931          1         5
5         231          2         6
6         444          2        43
7         333          3         9
8         931          3         3