Find the maximum value in each group of a big matrix

16 Ansichten (letzte 30 Tage)
Yaser Khojah
Yaser Khojah am 26 Apr. 2019
Kommentiert: Yaser Khojah am 26 Apr. 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 Kommentare
Jan
Jan am 26 Apr. 2019
Bearbeitet: Jan am 26 Apr. 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 am 26 Apr. 2019
Bearbeitet: Yaser Khojah am 26 Apr. 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

Melden Sie sich an, um zu kommentieren.

Akzeptierte Antwort

Jan
Jan am 26 Apr. 2019
Bearbeitet: Jan am 26 Apr. 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 Kommentare
Rik
Rik am 26 Apr. 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 am 26 Apr. 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

Melden Sie sich an, um zu kommentieren.

Weitere Antworten (0)

Kategorien

Mehr zu Creating and Concatenating Matrices finden Sie in Help Center und File Exchange

Tags

Community Treasure Hunt

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

Start Hunting!

Translated by