How to plot over certain range using if statements?

Question

DrWooo 2017-11-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/366848-how-to-plot-over-certain-range-using-if-statements

评论： DrWooo 2017-11-14

Hello,

I've inputted data from an excel file (defined here as B), and would like to generate two separate plots -- one where the value in column 7 is <25, and a second where the value in column 7 is >= 25.

So far, the code is:

s = B(1:18,7);
for x = B(1:18,5)        
    for y = B(1:18,12);  
        for i=1:length(B(1:18,7));
            if s(i)<25;  
              figure(1);
              subplot(3,1,1); 
              scatter(x,y); grid on;
              hold on
            elseif s(i)>=25;
              figure(2);
              subplot(3,1,1); 
              scatter(x,y); grid on;
              hold on
            end 
        end
     end
end

The plots are identical, and it appears that the code is checking that the value in column is < or >= 25, and then plotting all of (x,y). How do I limit it so it only plots (x,y) under those conditions separately?

Any advice or suggestions are appreciated.

Cheers

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Answer 1

KSSV 2017-11-14

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https://ww2.mathworks.cn/matlabcentral/answers/366848-how-to-plot-over-certain-range-using-if-statements#answer_290997

在 MATLAB Online 中打开

x = rand(100,1) ;
y = rand(100,1) ;
idx1 = y >= 0.5 ;
idx2 = y < 0.5 ;
figure
hold on
scatter(x(idx1),y(idx1),50,y(idx1),'s','filled')
scatter(x(idx2),y(idx2),50,y(idx2),'c','filled')
legend('data1','data2')

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DrWooo 2017-11-14

在 MATLAB Online 中打开

Thanks for the response. I was unfamiliar with the id function, and it's working great. The new code is:

for x = B(1:18,5)
  for y = B(1:18,12);
      idx1 = B(1:18,7) < 25;  %Decided to remove the s variable
      idx2 = B(1:18,7) >= 25;
        figure(2); subplot(3,1,1); 
        scatter(x(idx1),y(idx1));
        grid on; hold on
        lsline 
        mdl = fitlm(x(idx1),y(idx1));
        figure(3); subplot(3,1,1); 
        scatter(x(idx2),y(idx2));
        grid on; hold on
        lsline 
        mdl = fitlm(x(idx2),y(idx2));
end
end