[R] get mean of same elements in a data.frame

[Martin Batholdy]

Hi,


I have the following data.frame:

data.frame(x = c(1:10), y = rnorm(10,2,1), label = rep(c('a', 'b', 'c', 'd', 'e'),2))

in this data.frame there is a label-variable containing strings.
Each string is represented two times.

Now I would like to have the mean of the corresponding x (and y-values) for every unique label-element.

For the label 'a' for example there is an x value of 1 and 6.
So the resulting value should be 3.5.

How can I do this in R?