Getting all values in the same field for different entries within a structure

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Patrick
Patrick 2023-4-21
编辑： Stephen23 2023-4-22
Imagine I have a structure of students with certain info and their grades for different modules, looking like:
student(1).grades.math = 7;
student(2).grades.math = 9;
This student list might be any number. Is it possible to get all the different math grades in an array without a for-loop?
mathGrades = student.grades.math;
This doesn't seem to work and gives me the following error:
"Intermediate dot '.' indexing produced a comma-separated list with 2 values, but it must produce a single value when followed by subsequent indexing operations."

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Vilém Frynta
Vilém Frynta 2023-4-21
编辑：Vilém Frynta 2023-4-21
Ran in:
Try arrayfun (use function on the struct to extract the values into the array).
An example on your data:
% Your data
student(1).grades.math = 7;
student(2).grades.math = 9;
student(3).grades.math = 6;
% Use arrayfun to extract all the math grades into vector
mathGrades = arrayfun(@(x) x.grades.math, student)
mathGrades = 1×3
7 9 6
Hope my answer was useful. If it was, I'd be happy if you could accept my answer.

更多回答（1 个）

Stephen23
Stephen23 2023-4-22
编辑：Stephen23 2023-4-22
Ran in:
"Is it possible to get all the different math grades in an array without a for-loop?"
Of course.
The simple and efficient MATLAB approach is to use comma-separated lists:
https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them
https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html
student(1).grades.math = 7;
student(2).grades.math = 9;
student(3).grades.math = 6;
tmp = [student.grades];
out = [tmp.math]
out = 1×3
7 9 6
Avoid slow ARRAYFUN.

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