Find the highest value of y for each x value

Asked by Yaser Khojah

Yaser Khojah (view profile)

on 27 Apr 2019
Latest activity Edited by Yaser Khojah

Yaser Khojah (view profile)

on 29 Apr 2019
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);

Cedric Wannaz

Cedric Wannaz (view profile)

on 27 Apr 2019
What do you mean by "not happy with it"?

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Answer by Image Analyst

Image Analyst (view profile)

on 27 Apr 2019

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;

Yaser Khojah

Yaser Khojah (view profile)

on 29 Apr 2019
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)