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 = \         


        

Answer 1

I don't think you can handle conflicts well w/o a loop, nor do I think you'd need to avoid one. (although I suppose efficiency could be an issue w/ many many fields...)

I use a function I wrote a few years back called setdefaults.m, which combines one structure with the values of another structure, where one takes precedence over the other in case of conflict.

% SETDEFAULTS sets the default structure values 
%    SOUT = SETDEFAULTS(S, SDEF) reproduces in S 
%    all the structure fields, and their values,  that exist in 
%    SDEF that do not exist in S. 
%    SOUT = SETDEFAULTS(S, SDEF, OVERRIDE) does
%    the same function as above, but if OVERRIDE is 1,
%    it copies all fields of SDEF to SOUT.

function sout = setdefaults(s,sdef,override)
if (not(exist('override','var')))
    override = 0;
end

sout = s;
for f = fieldnames(sdef)'
    cf = char(f);
    if (override | not(isfield(sout,cf)))
        sout = setfield(sout,cf,getfield(sdef,cf));
    end
end

Now that I think about it, I'm pretty sure that the "override" input is unnecessary (you can just switch the order of the inputs) though I'm not 100% sure of that... so here's a simpler rewrite (setdefaults2.m):

% SETDEFAULTS2 sets the default structure values 
%    SOUT = SETDEFAULTS(S, SDEF) reproduces in S 
%    all the structure fields, and their values,  that exist in 
%    SDEF that do not exist in S. 

function sout = setdefaults2(s,sdef)
sout = sdef;
for f = fieldnames(s)'
    sout = setfield(sout,f{1},getfield(s,f{1}));
end

and some samples to test it:

>> S1 = struct('a',1,'b',2,'c',3);
>> S2 = struct('b',4,'c',5,'d',6);
>> setdefaults2(S1,S2)

ans = 

    b: 2
    c: 3
    d: 6
    a: 1

>> setdefaults2(S2,S1)

ans = 

    a: 1
    b: 4
    c: 5
    d: 6