r - How to sum a numeric list elements

Question

I'm wondering about an elegant way allowing to sum (or calculate a mean) a numeric values of a list. e.g.

x <- list( a = matrix(c(1,2,3,4), nc=2), b = matrix(1, nc=2, nr=2))

and want to get

x[[1]]+x[[2]] 

or a mean:

(x[[1]]+x[[2]])/2

Answer 1

You can use Reduce to successively apply a binary function to elements in a list.

Reduce("+",x)
     [,1] [,2]
[1,]    2    4
[2,]    3    5

Reduce("+",x)/length(x)
     [,1] [,2]
[1,]  1.0  2.0
[2,]  1.5  2.5