data cleaning - R: how to sum columns grouped by a factor?

Question

If I have a table like this:

user,v1,v2,v3
a,1,0,0
a,1,0,1
b,1,0,0
b,2,0,3
c,1,1,1

How to I turn it into this?

user,v1,v2,v3
a,2,0,1
b,3,0,3
c,1,1,1

Answer 1

In base R,

D <- matrix(c(1, 0, 0,
              1, 0, 1,
              1, 0, 0,
              2, 0, 3,
              1, 1, 1),
            ncol=3, byrow=TRUE, dimnames=list(1:5, c("v1", "v2", "v3")))
D <- data.frame(user=c("a", "a", "b", "b", "c"), D)
aggregate(. ~ user, D, sum)

Returns

> aggregate(. ~ user, D, sum)
  user v1 v2 v3
1    a  2  0  1
2    b  3  0  3
3    c  1  1  1