How to separate a vector into positive and negative vectors using a for loop?

clc;
x = [-3.6 10 3 -1 11.4 0 7 -9.5 2 15 -1 3];
for i = 1:length(x)
    if x(i) >= 0 
        x(i) = P
    elseif x(i) < 0
        x(i) = N
    end
end

This is what I have. It is obviously wrong but you should get the gist of it. It needs to be separated into two vectors: N and P

Answer 1

[Andrei Bobrov]

x = [-3.6 10 3 -1 11.4 0 7 -9.5 2 15 -1 3];
y = strings(numel(x),1);
for ii = 1:length(x)
    if x(ii) >= 0 
        y(ii) = "P";
    elseif x(ii) < 0
        y(ii) = "N";
    end
end

or

x = [-3.6 10 3 -1 11.4 0 7 -9.5 2 15 -1 3];
cn = 0;
cp = 0;
nn = numel(x);
p = zeros(nn,1);
n = zeros(nn,1);
for ii = 1:nn
    if x(ii) >= 0 
        cp = cp + 1;
        p(cp) = x(ii);
    else
        cn = cn + 1;
        n(cn) = x(ii);
    end
end
p = p(1:cp);
n = n(1:cn);

or

p = x(x >= 0);
n = x(x < 0);

[whyamiincollege]

both of your codes do not display an answr for me

Answer 2

[Image Analyst]

You're not supposed to assign x - that's a given constant. You're supposed to build N and P. So it will be more like

clc;
x = [-3.6 10 3 -1 11.4 0 7 -9.5 2 15 -1 3];
nIndex = 1;
pIndex = 1;
for i = 1:length(x)
    if x(i) >= 0 
        P(pIndex) = x(i);
        pIndex = .......
    elseif x(i) < 0
        N(nIndex) = x(i);
        nIndex = .............
    end
end    

See if you can complete your homework from the above.

[whyamiincollege]

keeps saying illegal use of elseif

[Image Analyst]

Tell me how you completed the lines I left for you to do. These lines:

pIndex = .......

and

nIndex = .............

What did you do to finish those lines? It's really trivial. What do you think you should do to those two variables to increment them to the next available index in the array?

Did you see where I said "See if you can complete your homework from the above." That means you have to do your homework yourself. I imagine your professor did not say "Ask this question on the internet and then post someone's working code as your own."

[whyamiincollege]

no need to get sassy bro. I played around with what i knew and nothing worked that's why i came here. I thought the "...." was part of the code, that was misunderstood. I will try again

[whyamiincollege]

I'm still not quite sure what to do here

[Image Analyst]

Increment means to add one. Here's the solution for one of them

nIndex = nIndex + 1;

You should be able to complete the one and only line left for you to complete. It's pretty analogous to the line above.

[whyamiincollege]

That is one of the things I tried. It still does not work

[whyamiincollege]

Don't worry about it though. I just did it a completely different way and it worked

[Image Analyst]

I tried it both before I posted, and after your last post, and it works perfectly fine.

The final line to get it to work is

pIndex = pIndex + 1;

Glad you found an alternate way that is 100% your own though - that's probably better as far as turning in graded homework goes.