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