extract specific points from a matrix of planar coordinates

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Tommaso Di Noto 2017-5-1

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回答： Tommaso Di Noto 2017-5-2

I have a 600x2 matrix with a series of planar points: x values on first column and y values on second one. How can I extract only the x values for which the corresponding y is null? Thank you!

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John Chilleri 2017-5-1

编辑：John Chilleri 2017-5-1

What type of variable is your matrix (i.e. cell)? Or if it's a normal matrix, how do you define null?

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Answer 1

KSSV 2017-5-1

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https://ww2.mathworks.cn/matlabcentral/answers/338164-extract-specific-points-from-a-matrix-of-planar-coordinates#answer_265188

在 MATLAB Online 中打开

Let A be your 600*2 matrix.

x = A(:,1) ;
y = A(:,2) ;
iwant = x(y==0) ;   % respective _x_ for which y=0

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Tommaso Di Noto 2017-5-2

Thank you! The passages are right; the only problem is that instead of 0 I have values such as 2e-04 or -4e-05. So if I write "==0" I get an empty vector. How can I solve this?

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