Find the highest value of y for each x value

Question

Yaser Khojah 2019-4-27

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/458869-find-the-highest-value-of-y-for-each-x-value

编辑： Yaser Khojah 2019-4-29

Book1.xlsx

Can anyone please help me with this quesiton. I have a big matrix where I’m only interested to plot the highest value of y for each x value. My x-axis ranges between 0 and 45 and I want the highest values for each one. So, I created the following code but I’m not happy with it. I also attached my data. Thank you for your time.

x       = MaT_All(:,18);
y       = MaT_All(:,17)
edges   = 200; % I used a number as 200 since I could not find the indexs of 0:45 in the original data (x) 
Group   = discretizediscretize(x ,edges); %
Result_y  = accumarray(Group, y , [], @max); % I got the highest values (y) but not sure how to find the corresponding  value in x 
scatter(Result_x ,Result_y) % how can i find Result_x 

I also tried this code

[G,TID] = findgroups(x);
Max_NPV = splitapply(@max,y),G);
scatter(TID,Max_NPV);

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Cedric 2019-4-27

What do you mean by "not happy with it"?

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Answer 1

Image Analyst 2019-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/458869-find-the-highest-value-of-y-for-each-x-value#answer_372556

在 MATLAB Online 中打开

How about (untested):

ux = unique(x)
hold on;
for k = 1 : length(ux) % For each unique x...
    % Find the max y for this x value.
    maxY = max(y == ux(k));
    % Plot that point.
    plot(ux(k), maxY, 'b.', 'MarkerSize', 10);
end
grid on;

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Yaser Khojah 2019-4-29

编辑：Yaser Khojah 2019-4-29

在 MATLAB Online 中打开

thanks fo your help but that does not give me what i'm looking for. I have this code but i still do not know how to find the index of the ymax?

x          = round(MaT_All(:,18),0);
y          = MaT_All(:,17);
[uv,~,idx] = unique(x);
ymax       = accumarray(idx,y,[],@max); %build matrix
[uv ymax];
figure
scatter(uv,ymax)
line(uv,ymax)