Averaging 3D matrix value and reshape

I have a Matrix named June21_Once_StillMat - the size of which is 15 x 41 x 40. I am trying to get the data from the colums 2 to 8 of the matrix une21_Once_StillMat to a new matrix A of size 15 x 8 x 40.

for j=1:15;
for k=1:8;
for i=1:40;
A(j,k,i)=June21_Once_StillMat(j,k+1,i);
end
end
end

I need to average the values of each row over i (40) from matrix A and populate that data to a new 3D matrix B of size 8 x 8 x 15. The third column of matrix B, B(k,3,j) will have the value obtained from the averaged value and the 4th column of matrix B, B(k,4,j) will be the standard error. I am not being able to figure this out.

Answer 1

[Yuan Li]

A = zeros(15,8,40);
A = June21_Once_StillMat(1:end,2:9,1:end);
A1 = mean(A,3);

then you will get a 15by8 matrix(mabe you need to rshape it), and the standard error comes from where?