Find maximum values related to index

Hello community,

I am trying to write a for loop to find the maximum values in column 2 for each group variable in column 1. I tried a for loop to no avail. Any help would be appreciated.

The solution should result in a maximum value, corresponding row index, for each group variable in column 1. So, the solution should yield 1) the group index associated with stests(:,1) 2) maximum values of stests(:,2) per group index 3) the row index of stests corresponding to each max value result

I attached a 2418x2 matrix called stests.

I apologize ahead of time for my lack of proper data science language.

Very much appreciated.

Regards, Mark

Answer 1

[jonas]

Ideal job for findgroups and splitapply.

VAL is the max value in each group, located at id_l (local group index). For example, id_l=2 if max value is second value in group.

data=xlsread('stests.xlsx');

%%Find max value and local index
G=findgroups(data(:,1));
[VAL,id_l]=splitapply(@max,data(:,2),G);

%%Find global index
[~,b]=unique(data(:,1));
id_g=[id_l+b]-1;

%Store results
out=[VAL,id_g]

[mark cejas]

Thank you Jonas. I appreciate this elegant solution and the intro to the great function. Haven’t checked yet, but it looks great!!!

[jonas]

You're welcome, let me know if you encounter some bug.