How does one plot only the maximum y value for an x value with multiple y values?

I have two vectors (y4 and T4) and need to plot y4 on the x-axis and T4 on the y-axis. The only problem is that there exists multiple values of T4 for each value of y4, so how can I only plot the highest of the T4 values for each y4? I have attached my two vectors for reference.

Answer 1

[Star Strider]

The accumarray function is perfect for this:

D = load('y4-T4.mat');
T4 = D.T4;                                                  % Define ‘T4’
y4 = D.y4;                                                  % Given ‘y4’

[Uy4,~,Ix] = unique(y4);                                    % Unique Values Of ‘y4’
T4Max = accumarray(Ix, T4, [], @max);                       % Maximum Values Of ‘T4’
y4T4 = [Uy4, T4Max];                                        % Matrix OF Unique & Corresponding Maximum Values 

figure
plot(Uy4, T4Max)
grid
xlabel('y4')
ylabel('T4')
ylim([min(ylim) 850])

Other options are possible, including the mean, median, standard deviation, and others, just by changing the function call in accumarray.

[Geoff Doback]

Worked perfectly - thanks!

[Star Strider]

As always, my pleasure!

Answer 2

[Basil C.]

Hi Geoff,

After seeing the data you provided im assuming the data set it something like

y4=[5     5     4     4     3     3     2     2     2]; 
t4=[1     2     3     4     5     6     7     8     9];  % this is not the actual data but only for better...
                                                           % understanding of how I see your problem

And the solution you are searching for is like

y4=     [ 5 4 3 2]
answer= [ 2 4 6 9] % the maximum value of each t4 for a unique y4 value

Then the below solution should help you

N = diff([0 find(diff(y4)) numel(y4)]) %NOTE y4 should be a horizontal vector
answer=[];
for i=1:numel(N)
s=sum(N(1:i));
k=T4(s-N(i)+1:s);
answer=[answer,max(k)];
end

Y4=unique(y4)
answer