How to run a for-loop with different dimesions?

Let A be a 20 by 1 array. I can separately compute

B_1=mean(A(1:6, 1:1)),

B_2=mean(A(7:15, 1:1)), and

B_3=mean(A(16:20, 1:1)).

How can I program this job using the loop command with respect to different dimensions?

Answer 1

[Walter Roberson]

starts = [1 7 16];
stops  = [6, 15, 20];
n = length(starts);
B = zeros(1,n);
for K = 1 : n
    B(K) = mean(A(starts(K):stops(K), 1));
end

[Wan-Yi Chiu]

Thank you very much.