how to assign same value according to each subgroup

Question

Hyein Han 2020-5-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/538683-how-to-assign-same-value-according-to-each-subgroup

评论： Ameer Hamza 2020-5-31

采纳的回答： Ameer Hamza

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!

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Answer 1

Ameer Hamza 2020-5-31

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/538683-how-to-assign-same-value-according-to-each-subgroup#answer_443375

编辑：Ameer Hamza 2020-5-31

在 MATLAB Online 中打开

Try this

M = [
         1
         2
         1
         2
         1
         1
         2
         1
         2
         3
         1
         2
         3
         2
         1
         1
         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

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Hyein Han 2020-5-31

WOW, yes it really worked. I couldn't proceed further from splitapply function, and your "ClassID2 = max_vals(grps)" command helped me to resolve this. Thanks a lot!