Find the maximum value in each group of a big matrix

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)];

[Jan]

What does "group them by a certain way" mean? What exactly are "the indices of all the maximum points"? Please post a small example or define the procedure exactly.

[Yaser Khojah]

So for example, my sortedMatrix is as below. Now The group is the first column and I would like to fix the max of each group (1,1,3 and 4). So Group 1 max is 3.7

1	0.773590911304249
1	3.71378812760058
3	11.1735613881447
4	15.3263030828475
NaN	-8.63652821988714
NaN	-12.1411704361541
NaN	-11.1350074148676
NaN	-0.0684932810334807
NaN	-7.69665913753682
NaN	-2.25584402271252

[Yaser Khojah]

so I should have something the below and I want to know ther indices in the original from the original data

1	3.71378812760058
3	11.1735613881447
NaN	-0.0684932810334807

[Jan]

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]

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

Answer 1

[Jan]

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.

[Rik]

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]

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))