Standard deviation over a list of matrices in R

Question

I have a list in which each element is a matrix.

set.seed(123)



m1 <- matrix(sample(c(1:10), size = 9, replace = TRUE), ncol = 3, nrow = 3)

m2 <- matrix(sample(c(1:10), size = 9, replace = TRUE), ncol = 3, nrow = 3)

m3 <- matrix(sample(c(1:10), size = 9, replace = TRUE), ncol = 3, nrow = 3)



m <- list(m1, m2, m3)

m

[[1]]

      [,1] [,2] [,3]

[1,]    3    9    6

[2,]    8   10    9

[3,]    5    1    6



[[2]]

     [,1] [,2] [,3]

[1,]    5    7    9

[2,]   10    6    3

[3,]    5    2    1



[[3]]

     [,1] [,2] [,3]

[1,]    4    7    7

[2,]   10    7    8

[3,]    9   10    6

I want to calculate the standard deviation of each pair considering all three matrices. So for cell [1,1] the standard deviation would be:

sd(c(3, 5, 4))

My final matrix should look like this:

     [,1] [,2] [,3]

[1,] 1.00 1.15 1.53

[2,] 1.15 2.08 3.21

[3,] 2.31 4.93 2.89

How can I achieve this in R without a loop over all three matrices?

Many thanks in advance.

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Answer 1

It is better to convert this to array by unlisting the list to a vector, convert it to a 3D array and get the sd with apply

round(apply(array(unlist(m), c(3, 3, 3)), c(1,2), sd),2)
#    [,1] [,2] [,3]
#[1,] 1.00 1.15 1.53
#[2,] 1.15 2.08 3.21
#[3,] 2.31 4.93 2.89

Standard deviation over a list of matrices in R

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