How to copy field contents of one struct to another?

Hi all,

I have got two structs, A and B. B has a subset of the fields of A:

A.f1 = 1;
A.f2 = 2;
A.f3 = 3;

B.f1 = 4;
B.f2 = 5;

Now I want to copy all field content of B to the corresponding fields of struct A, leaving the other fields of A unchanged:

A.f1 = B.f1;
A.f2 = B.f2;
% A.f3 == 3 untouched

Is there a simply way to achieve this for arbitraty structs A and B, considering that B's field names are always a subset of A's field names?

Thank you very much, Ralf

Answer 1

[Guillaume]

Iterate over the fieldnames of B to copy them using dynamic field names:

A = struct('f1', 1, 'f2', 2, 'f3', 3);
B = struct('f1', 4, 'f2', 5);
for fn = fieldnames(B)'
   A.(fn{1}) = B.(fn{1});
end

[Chris]

B.(fn{1})

returns the first value. If you have more than one value or data type (e.g., table) in the field, put this term in curly brackets { }:

A = struct('f1', 1, 'f2', 2, 'f3', 3);
B = struct('f1', 4, 'f2', 5);
for fn = fieldnames(B)'
    A.(fn{1}) = {B.(fn{1})};
end

[Stephen23]

"If you have more than one value or data type (e.g., table) in the field, put this term in curly brackets { }:"

How many values there are in one field is irrelevant. It actually depends on how many elements B has:

https://www.mathworks.com/matlabcentral/discussions/tips/847976-tutorial-comma-separated-lists-and-how-to-use-them

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

Depending on the data types and array sizes the functions HORZCAT, VERTCAT etc may also be useful.