# [R] how to calculate means of matrix elements

Gabor Grothendieck ggrothendieck at gmail.com
Wed May 20 13:41:58 CEST 2009

```In that case use a modification of Jim's solution:

a <- array(cbind(mat1, mat2, mat3), c(3, 3, 3))
apply(a, 1:2, mean, na.rm = TRUE)

On Tue, May 19, 2009 at 8:49 AM, dxc13 <dxc13 at health.state.ny.us> wrote:
>
> Easy enough.  What if some of the matrix elements contained missing values?
> Then how could you still calculate the means?  Example code below:
> mat1 <- matrix(c(1,2,3,4,5,NA,7,8,9),3,3)
> mat2 <- matrix(c(NA,6,1,9,0,5,8,2,7),3,3)
> mat3 <- matrix(c(5,9,1,8,NA,3,7,2,4),3,3)
>
>
> Gabor Grothendieck wrote:
>>
>> Try this:
>>
>> (mat1 + mat2 + mat3) / 3
>>
>> On Mon, May 18, 2009 at 8:40 PM, dxc13 <dxc13 at health.state.ny.us> wrote:
>>>
>>> useR's,
>>> I have several matrices of size 4x4 that I want to calculate means of
>>> their
>>> respective positions with.  For example, consider I have 3 matrices given
>>> by
>>> the code:
>>> mat1 <- matrix(sample(1:20,16,replace=T),4,4)
>>> mat2 <- matrix(sample(-5:15,16,replace=T),4,4)
>>> mat3 <- matrix(sample(5:25,16,replace=T),4,4)
>>>
>>> The result I want is one matrix of size 4x4 in which position [1,1] is
>>> the
>>> mean of position [1,1] of the given three matrices.  The same goes for
>>> all
>>> other positions of the matrix.  If these three matrices are given in
>>> separate text files, how can I write code that will get this result I
>>> need?
>>>
>>> dxc13
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>
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