avoiding for loop

Hi..

I really want to avoid for loop in my program because it takes longer time if the array is too big.

For example i have two arrays. Let say A and B

   A=[1 2 3 4 5];
   B=[4 5 6 2 1];

and the outcome array C should be like this C=[5 7 9 -2 -4]

what i did was:

 for i=1:length(B)
   if (B(i)>A(i))
       C(i)=B(i)+A(i);
   else
       C(i)=B(i)-A(i);
   end
   end

p/s: actually my function is a bit different but the principle is same.

Answer 1

[Jan]

And another solution:

A = [1 2 3 4 5]';
B = [4 5 6 2 1]';

index     = B > A;
C(index)  = B(index)  + A(index);
nindex    = ~index;
C(nindex) = B(nindex) - A(nindex);

And another one:

f = 2 * (B > A) - 1;
C = B + f .* A;

[Andrei Bobrov]

+1, for "another one"

Answer 2

[Andrei Bobrov]

out = B + sign(B - A).*A;

EDITED on Jan's comment

out = (B~=A).*B + sign(B - A).*A;

[Jan]

+1. A general suggestion for sign() compared to "if A>B, else, end": Check if the A==B case is correct!

Answer 3

[Wayne King]

   A=[1 2 3 4 5]';
   B=[4 5 6 2 1]';
   C = [A B];
   D = C(:,2)-C(:,1);
   out = [sum(C(D>0,:),2); diff(C(D<=0,:),[],2)]

Answer 4

[Muhammad Affandi]

thanks..thats great.. now i have so many alternatives..