How to extract elements from each dimension of a 3D matrix and put it in a vector.

I have a 3D matrix that is

B = (31, 37, 91);

I would like to extract all the elements from each dimension, and place it in a vector, then take the variance of the vector.

In the end, I would like to make a vector of all of the variances.

For example,

C = [Var1; Var2; ... Var91];

Below is what I have tried so far, but I am curious if there is a way without doing each dimension individually.

Thanks in advance!

F1 = B(:,:,1);    
F1v = F1(:);     %vector
Var1 = var(F1v);

F2 = B(:,:,2);    
F2v = F2(:);     %vector
Var2 = var(F2v);

Answer 1

[Guillaume]

Sure, you just have to type the same code 91 times...

As you can guess, that's not a viable approach. If you start numbering variables, you're doing it wrong.

If you're on R2018b or later, it's trivial to obtain your vector:

V = var(B, 0, [1 2]);  %requires R2018b or later

Optionally, you can squeeze the result, but having a vector along the page makes more sense.

In earlier versions, var can only operate on one dimension at once, so you must first reshape your matrix into an Nx91 matrix:

V = var(reshape(B, [], size(B, 3)))

[Anna M]

Thanks! The reason I am numbering my variables is because I use the individual vectors of each dimension in other calculations. However, I am a beginner, so I am working on consicing my code and becoming less redundant..

Your suggestion gave me exactly what I needed. I do have a question, what does the [1 2] mean in: V = var(B, 0, [1 2]);

I did not want to use that if I did not fully understand.

Edit*: I see it now! I read it means for dimensions 1 and 2. Thanks again