Mean of each element of a list of matrices

Question

I have a list with three matrixes:

a<-matrix(runif(100))
b<-matrix(runif(100))
c<-matrix(runif(100))

mylist<-list(a,b,c)

I wou

Answer 1

Your question is not clear.

For the mean of all elements of each matrix:

sapply(mylist, mean)

For the mean of every row of each matrix:

sapply(mylist, rowMeans)

For the mean of every column of each matrix:

sapply(mylist, colMeans)

Note that sapply will automatically simplify the results to a vector or matrix, if possible. In the first case, the result will be a vector, but in the second and third, it may be a list or matrix.

Example:

a <- matrix(1:6,2,3)
b <- matrix(7:10,2,2)
c <- matrix(11:16,3,2)
mylist <- list(a,b,c)

> mylist
[[1]]
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

[[2]]
     [,1] [,2]
[1,]    7    9
[2,]    8   10

[[3]]
     [,1] [,2]
[1,]   11   14
[2,]   12   15
[3,]   13   16

Results:

> sapply(mylist, mean)
[1]  3.5  8.5 13.5

> sapply(mylist, rowMeans)
[[1]]
[1] 3 4

[[2]]
[1] 8 9

[[3]]
[1] 12.5 13.5 14.5

> sapply(mylist, colMeans)
[[1]]
[1] 1.5 3.5 5.5

[[2]]
[1] 7.5 9.5

[[3]]
[1] 12 15