Find the maximum value in each group of a big matrix

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Yaser Khojah
Yaser Khojah el 26 de Abr. de 2019
Comentada: Yaser Khojah el 26 de Abr. de 2019
I have a big matrix and I'm looking for an easy way to group them by a certain way then find the maximum in each group. I have created this code but I got stuck. Anyway to help please. I need to know the indexes of all the maximum points to extract more information from the big matrix.
data = randn(10,1)*10;
edges = 0:5:35';
Y = discretize(data,edges);
[B,I] = sort(Y);
SortedMatrix = [B data(I)];
  5 comentarios
Jan
Jan el 26 de Abr. de 2019
Editada: Jan el 26 de Abr. de 2019
So is sortedMatrix your actual input data? Or do you want to process data, which is set to a random array for a demonstration?
It would be easier, if you avoid to create the NaNs, e.g. by adding a final edge Inf. Then splitapply(@max, data(I), B) would solve the problem.
Yaser Khojah
Yaser Khojah el 26 de Abr. de 2019
Editada: Yaser Khojah el 26 de Abr. de 2019
I have attached my data (Data) and I will explain what I'm trying to do on this file.
edges = 0:5:35';
% i want to split column 18 based on edges
Y = discretize(Data(:,18),edges);
% this is see the new data sorted
[B,I] = sort(Y);
SortedMatrix = [B Data(I,:)];
% How can i find the max in every edges. It might be there is more than a max but I want to know how they are related to the original data so I need their indexs in the original data

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Jan
Jan el 26 de Abr. de 2019
Editada: Jan el 26 de Abr. de 2019
data = randn(10,1)*10;
edges = [-Inf, 0:5:35, Inf];
Y = discretize(data, edges);
Result = accumarray(Y, data, [], @max)
I'm confused that this does not work reliably with splitapply:
Result = splitapply(@max, data, Y)
It fails with an error message, if an interval is empty:
For N groups, every integer between 1 and N must occur at least
once in the vector of group numbers.
  2 comentarios
Rik
Rik el 26 de Abr. de 2019
I was thinking way too complicated here. This was the start of my idea:
nanflag=false;
if any(isnan(B))
replaceNaN=max(B)+1;
B(isnan(B))=replaceNaN;
nanflag=true;
end
b=accumarray(B,Y,[],@max,NaN);
After which removal of empty lines (and putting back the NaN) to get to the desired output should be easy.
Yaser Khojah
Yaser Khojah el 26 de Abr. de 2019
Dear Jan and Rik. Thank you for your help. I'm sorry if i made you both get confused
So, here what I want to do from what I asked earlier. I have this big file (MAT_All). I would like to create this thick line that shows the maximum at every x-axis. So, that is why I was looking for maximum for every interval but not sure if i will get this from what I asked earlier. Any idea?
scatter(MaT_All(:,18), MaT_All(:,17))
Capture.JPG

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