MATLAB: How to use a for loop to return a vector

for loopvector

Hey everyone, I've been using matlab for about a month, so this might be a pretty simple question.
I have a vector x=[-3.5 -5 6.2 11 0 8.1 -9 0 3 -1 3 2.5], and I want to make two other vectors from it using a for loop. The first contains the positive elements of x, and the second contains the negative elements of x. I can get it to return individual elements, but not vectors. Your help is greatly appreciated, I've been trying to figure this out for a couple hours.
Heres my code
x=[-3.5 -5 6.2 11 0 8.1 -9 0 3 -1 3 2.5];
n=length(x);
for k=1:n
if x(k)>0
P=x(k)
 elseif 
x(k)<0
 N=x(k)
    end
end

Best Answer

Hi Adam,
you actually don't need a loop:
P = x(x > 0);
N = x(x < 0);
P =
      6.2000   11.0000    8.1000    3.0000    3.0000    2.5000
N =
     -3.5000   -5.0000   -9.0000   -1.0000
If you want to use a loop, you need to assign an index to P and N, otherwise the loop will erase the current value at every iteration. Here's an example;
P = zeros(1,length(x)); % Initialize a vector P of length equal to that of x. After the loop we get rid of the 0 values.
N = P; same thing for N.
for k=1:length(x)
      if x(k)>0 
          P(k) =x(k);
      elseif x(k)<0
          N(k)=x(k);
      end
  end
P(P==0) = []; % Remove values equal to 0
N(N==0) = [];
Related Question