operation between 2 vectors by Indexing

Question

Lila wagou 2017-4-8

回答： Star Strider 2017-4-8

Dear, I looking to doing a operation (summation for example) between two vectors but the elements indexing are stored in others two vectors:

vectors to summation

A = [10 25 12.5 4 -7.5];
B = [0.05 33.5 -20 12.25 0.65];

Indexing vectors

Aind = [1 4 5 4]; % index for A vector
Bind = [3 2 1 5]; % index for B vector

for result i must have

C(1) = A(1)+B(3) = 10+(-20)
C(2) = A(4)+B(2) = 4+33.5
C(3) = A(5)+B(1) = -7.5+0.05
C(4) = A(4)+B(5) = 4+0.65

I am blocked

for i = 1 : length(Aind)
    C(i) = A(Aind ?)+B(Bind ?)
end

Answer 1

Star Strider 2017-4-8

No loop necessary. You have all the infromation you need in ‘A’, ‘B’, and the index vectors:

C = A(Aind) + B(Bind)
C =
          -10         37.5        -7.45         4.65