access array multiple times and calculate some value

Question

dleal 2022-7-28

回答： David Hill 2022-7-28

Hi all, I would like to know if there's a faster way that using a foor loop for this:

a = rng(99);
A = randn(1,100);
B = [20 23; 30 37; 51 55; 78 100 ];

For each row B, I would like to slice A from the first column to the second column value, and then apply some function, for example, sum.

So for example, the first computation would be sum(A(20:23)), then sum(A(30:37)) ... sum(A(78:100)).

The for loop would be:

for ii = 1:size(B,1)
    sum(A(B(ii,1) : B(ii,1) );
end

Could I program this such that it results in a faster calculation?

Answer 1

David Hill 2022-7-28

Shorter way to write it, but will not improve speed.

s=arrayfun(@(x)sum(A(B(x,1):B(x,2))),1:size(B,1));