MATLAB: How to assign same value according to each subgroup

Question

Hello, I'd like to generate new variable, say, classid2

My dataset looks like the following:

school classid

11005 1

11005 2

11006 1

11006 2

11009 1

11010 1

11010 2

11013 1

11013 2

11013 3

11015 1

11015 2

11015 3

11017 2

11017 1

11020 1

11020 2

—————————————————-

each school has different number of classes, (can be 1, 2, or 3) and Ssize is number of students each class has. What I want is new variable classid2, which is the maximum value of classid for each school such as the following,

school classid classid2

11005 1 2

11005 2 2

11006 1 2

11006 2 2

11009 1 1

11010 1 2

11010 2 2

11013 1 3

11013 2 3

11013 3 3

11015 1 3

11015 2 3

11015 3 3

11017 2 2

11017 1 2

11020 1 2

11020 2 2

I cannot come up with how to state using if or for loop, or maybe rearrange the arrays?

Thanks in advance!

Answer 1

Try this

M = [
11005           1
11005           2
11006           1
11006           2
11009           1
11010           1
11010           2
11013           1
11013           2
11013           3
11015           1
11015           2
11015           3
11017           2
11017           1
11020           1
11020           2];
school = M(:,1);
classID1 = M(:,2);
grps = findgroups(school);
max_vals = splitapply(@max, classID1, grps);
classID2 = max_vals(grps);

Result

>> classID2
classID2 =
     2
     2
     2
     2
     1
     2
     2
     3
     3
     3
     3
     3
     3
     2
     2
     2
     2