How to sum elements in a vector according to the location information from another vector?

Hello,

I have a vector lets say V=[3 5 3 7 1 7 9 3 9 2 0 3 9]

and another vector that is indicating the which elements that are needed to be summed. Lets say L=[1 4 5 6 8]

So my output should be the sum of first,fourth,fifth,sixth and eighth elements in V. I.e. sum=3+7+1+7+3=21

How can this code be to get the sum value?

Thanks in advance!

Answer 1

[Ahmet Cecen]

 sum(V(L))

Answer 2

[Muhammad Usman Saleem]

I have convert this question to a function. Please check it and tell me if not working

function sum1=runsum(V,L)
runsum=0;
for i=1:length(L)
    runsum=runsum+V(L);
end
sum1= runsum;
end

[Ekin]

Seems working as well, but check Ahmet's answer for short code. Thanks

[Muhammad Usman Saleem]

my code seem working more efficiently than other. It depend on your own requirement...

[Stephen23]

@Muhammad Usman Saleem: not only is your code ten times slower than Ahmet Cecen's, your code also does not give the correct answer:

>> [A,B] = test(1e5)
Elapsed time is 0.183132 seconds. % Ahmet's code (fast)
Elapsed time is 1.775014 seconds. % Your code (slow)
A =
    21                            % Ahmet's code (correct)
B =
    15    35     5    35    15    % Your code (incorrect)

Your code has one obvious bug (keyword: indexing), and the fact that its output is obviously incorrect shows that you never tested your code. It is also pointless to reinvent perfectly good inbuilt functionality.

The test file is here, so you can try it yourself (I used R2012b):