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

Question

Patrick 2023-4-21

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https://ww2.mathworks.cn/matlabcentral/answers/1951223-getting-all-values-in-the-same-field-for-different-entries-within-a-structure

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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Answer 1

Vilém Frynta 2023-4-21

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编辑：Vilém Frynta 2023-4-21

在 MATLAB Online 中打开

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.

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Patrick 2023-4-21

Thank you, this was what I was looking for!

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Answer 2

Stephen23 2023-4-22

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https://ww2.mathworks.cn/matlabcentral/answers/1951223-getting-all-values-in-the-same-field-for-different-entries-within-a-structure#answer_1220873

编辑：Stephen23 2023-4-22

在 MATLAB Online 中打开

"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