averaging a list of matrices element wise

If you don't have any NAs, then one way is:

n <- 3
r <- 5
s <- 6
raw <- lapply(seq_len(n), function(i){
   matrix(rnorm(r * s), ncol = r)
})

Reduce("+", raw) / length(raw)


I hope it helps.

Best,
Dimitris


On 11/5/2012 11:32 AM, ONKELINX, Thierry wrote:

Dear all,

I have a list of n matrices which all have the same dimension (r x s). What would be a fast/elegant way to calculate the element wise average? So result[1, 1] <- mean(c(raw[[1]][1, 1] , raw[[2]][1, 1], raw[[...]][1, 1], raw[[n]][1, 1]))

Here is my attempt.

#create a dummy dataset
n <- 3
r <- 5
s <- 6
raw <- lapply(seq_len(n), function(i){
   matrix(rnorm(r * s), ncol = r)
})

#do the calculation
result <- array(dim = c(dim(raw[[1]]), length(raw)))
for(i in seq_along(raw)){
   result[,,i] <- raw[[i]]
}
result <- apply(result, 1:2, mean)


Best regards,

Thierry

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
Thierry.Onkelinx at inbo.be
www.inbo.be

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