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

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whyamiincollege 2019-3-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/453580-how-to-separate-a-vector-into-positive-and-negative-vectors-using-a-for-loop

评论： Image Analyst 2019-4-1

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

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回答（2 个）

Andrei Bobrov 2019-3-31

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https://ww2.mathworks.cn/matlabcentral/answers/453580-how-to-separate-a-vector-into-positive-and-negative-vectors-using-a-for-loop#answer_368340

编辑：Andrei Bobrov 2019-3-31

在 MATLAB Online 中打开

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

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);

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

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whyamiincollege 2019-3-31

both of your codes do not display an answr for me

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Image Analyst 2019-3-31

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/453580-how-to-separate-a-vector-into-positive-and-negative-vectors-using-a-for-loop#answer_368341

在 MATLAB Online 中打开

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    