Calculating mean of multiple matrices in R

Update: anyone preferring base-R will want Reduce instead (please upvote @thelatemail below):

Reduce(`+`, x) / length(x)

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Original:

I think there's a better solution to this now, courtesy of purrr::reduce.

require(purrr)
x = list(volcano+10, volcano-15, volcano-5)
v = reduce(x, `+`) / length(x)
image(v)

Combine them into an array and use apply:

A <- matrix(c(2,4,3,5), 2)
B <- matrix(c(6,8,7,9), 2)

X <- list(A, B)
Y <- do.call(cbind, X)
Y <- array(Y, dim=c(dim(X[[1]]), length(X)))

apply(Y, c(1, 2), mean, na.rm = TRUE)
#     [,1] [,2]
#[1,]    4    5
#[2,]    6    7

If apply is not efficient enough, you can use colMeans (which provides NA handling) with aperm:

colMeans(aperm(Y, c(3, 1, 2)), na.rm = TRUE)
#     [,1] [,2]
#[1,]    4    5
#[2,]    6    7