在R中矢量化循环

Question

There must be a simple way to vectorize the following loop in R, but I can't see it.

w <- numeric(10)
z <- rnorm(20)
v <- c(sample(1:10,10),sample(1:10,10)) #Random ordering of c(1:10,1:10)
for(i in 1:10)
    w[i] <- sum(z[v==i])

Answer 1

另一种方法

w = rowsum(z, v)

Answer 2

You could use aggregate:
aggregate(z, by=list(v), sum)