Question

I am working with arrays of structs and objects in Matlab. I want to set properties for all the members of a certain array as fast as possible.

For the problem of setting a certain struct field, I reached a solution that involves using arrayfun and setfield. The following works like a charm:

myStru.id = 0;
myStru.name = 'blah';
arrayStru = repmat(myStru,10,1);  % Array of 10 elements. All of them have id=0
arrayStru = cell2mat( arrayfun( @(x,y)setfield(x,'id',y), arrayStru, (1:10)', 'UniformOutput', false ) ); % ids ranging from 1 to 10 :D

The problem is that, for objects, this does not work. I understand that setfield is for structures, so I have tried some other alternatives. The most excruciating error pops out when I try the following:

arrayfun( @(x,y) eval(['x.id=y;']), arrayOfObjects, arrayOfValues, 'UniformOutput', false );

(The class is a very simple one, which accepts empty constructor and has a real public property called ‘id’). It results in:

Error using setFieldOfStructArray>@(x,y)eval(['x.id=y;']) (line 17)
Error: The expression to the left of the equals sign is not a valid target for an
assignment.

ALTHOUGH if I put a breakpoint in that line, it seems that the expression can be executed with the expected effects.

My two (three) questions:

• Why does the above solution fail? How can I get that to work?
• My final goal is to set properties fast and simple in arrays of objects. Which is the best technique for this?

(Note: I can write loops, but I always feel itchy when I have to do that :P)

Answer 1

I think the problem may be that your propety may be readonly because setfield works also for classes.

Anyway there is some alternative, if your class inherit from hgsetget you can use set instead of setfield.

You can also use

subsasgn(x,struct('type','.','subs','id'),y) 

instead of

setfield(x,'id',y)