MATLAB Answers

Find that max and its index for data with multiple data values per index

4 views (last 30 days)
Hello,
I looked around and found similar questions that have been answered (here 1 and here 2) but not sure how to find the max y value at each x value and its index. It might contain ore than an index of there is two max values.
so, I need to find the max, its index so I can create related to the original data in Sorted_ENP
Thanks in advance.
x = round(Sorted_ENP(:,end),1);
y = Sorted_ENP(:,end-1);
[uv,~,idx] = unique(x);
ymax = accumarray(idx,y,[],@max)
ymax_idx = accumarray(idx,y,[],@(x) maxidx(x))
% how can i find the index of ymax
All_data = Sorted_ENP(ymax_idx,:) % i want the matrix after the max values have been selected.
function ymax_idx = maxidx(x)
[~, ymax_idx] = max(x);
end

  0 Comments

Sign in to comment.

Accepted Answer

Guillaume
Guillaume on 6 Feb 2020
There a many functions you can use for this (accumarray, splitapply, etc.) but with any of them you're going to have to build a vector of row index to your grouping function.
[group, value] = findgroup(round(Sorted_ENP(:,end),1));
rows = (1:size(Sorted_ENP, 1))';
max_idx = splitapply(@custom_max, Sorted_ENP(:,end-1), rows, group)
%for pretty display
array2table([value, max_idx], 'VariableName', {'x', 'max', 'max_idx'})
With
function max_idx = custom_max(vector, rowindices)
%takes a column vector and a vector of the same length indicating which rows of the original matrix, the values of the vector come form
%return a 2 element row vector, the max value, and the location with regards to the original row index of that max value
[maxval, loc] = max(vector);
max_idx = [maxval, rowindices(loc)];
end

  1 Comment

Yaser Khojah
Yaser Khojah on 6 Feb 2020
thank you so much for your help. It is finally working. I truely appericate your help.

Sign in to comment.

More Answers (0)

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by