How to loading a vector with values from a logical index

I have a vector, Vin, of length m. I also have a logical vector, Idx, to select indices to work on (subset size n < m). I can operate on Vin(Idx) and get Vdata of length n. This is all good. But now I want to generate a new Vout vector that is filled with the values from Vdata at the appropriate index. This can be accomplished by the following code snippet.

Vout=zeros(length(Vin));
k = 1;
for j = 1:length(Vin)
  if Idx(j)
      Vout(j) = Vdata(k);
      k = k + 1;
  end
end

This seems verbose ? Is there a more efficient or correct way of doing this? i want the output vector to be of length m, not n

Answer 1

[Sara]

Vout = Vin(Idx)

[Timothy Carnahan]

does not load Vdata into Vout - and I want Vout of size M NOT N.

[Sara]

Vout = zeros(length(Vin),1);
Vout(Idx) = Vin(Idx);

[Timothy Carnahan]

Ah - yes

Vout = zeros(length(Vin));
Vout(Idx)=Vdata;

[Sara]

You may want to do zeros(length(Vin),1), otherwise you get a square matrix instead of a 1d array for Vout