What are some efficient ways to combine two structures in MATLAB?

Question

I want to combine two structures with differing fields names.

For example, starting with:

A.field1 = 1;
A.field2 = 'a';

B.field3 = 2;
B.field4 = 'b';

I would like to have:

C.field1 = 1;
C.field2 = 'a';
C.field3 = 2;
C.field4 = 'b';

Is there a more efficient way than using "fieldnames" and a for loop?

EDIT: Let's assume that in the case of field name conflicts we give preference to A.

Answer 1

Without collisions, you can do

M = [fieldnames(A)' fieldnames(B)'; struct2cell(A)' struct2cell(B)'];
C=struct(M{:});

And this is reasonably efficient. However, struct errors on duplicate fieldnames, and pre-checking for them using unique kills performance to the point that a loop is better. But here's what it would look like:

M = [fieldnames(A)' fieldnames(B)'; struct2cell(A)' struct2cell(B)'];

[tmp, rows] = unique(M(1,:), 'last');
M=M(:, rows);

C=struct(M{:});

You might be able to make a hybrid solution by assuming no conflicts and using a try/catch around the call to struct to gracefully degrade to the conflict handling case.