Question

I have a vector

V=[ 1 2 3 5 9];

and would like to multiply it like this:

newVect=zeros(1,length(V));

for i=1:length(V)

    if V(i)==1
       newVect(i)=V(i)*somevaluex
    elseif V(i)==5
       newVect(i)=V(i)*somevaluey
    else
       newVect(i)=V(i);
end

This seems cumbersome as I’m actually dealing with arrays with 10000 elements. Can this be replaced by vectorisation somehow?

Answer 1

You can do that:

newVect = V .* (   someValuex.*(V==1) +  someValuey.*(V==5) + V.*( (V~=1) & (V~=5) ) )

or a bit faster:

newVect=V;
newVect(V==1)=V(V==1)*someValuex;
newVect(V==5)=V(V==5)*someValuey;