Better code for accessing fields in a matlab structure array? - matlab

Question

I have a matlab structure array Modles1 of size (1x180) that has fields a, b, c, ..., z.
I want to understand how many distinct values there are in each of the fields. i.e.
max(grp2idx([foo(:).a]))
The above works if the field a is a double. {foo(:).a} needs to be used in the case where the field a is a string/char.
Here's my current code for doing this. I hate having to use the eval, and what is essentially a switch statement. Is there a better way?
names = fieldnames(Models1);
for ix = 1 : numel(names)
className = eval(['class(Models1(1).',names{ix},')']);
if strcmp('double', className) || strcmp('logical',className)
eval([' values = [Models1(:).',names{ix},'];']);
elseif strcmp('char', className)
eval([' values = {Models1(:).',names{ix},'};']);
else
disp(['Unrecognized class: ', className]);
end
% this line requires the statistics toolbox.
[g, gn, gl] = grp2idx(values);
fprintf('%30s : %4d\n',names{ix},max(g));
end

Answer 1

Indeed, there is a better way. Surprisingly, MATLAB allows you to access the struct fields using a key string without eval, for instance:
Models1(1).(names{ix})
so instead, you can write this:
className = class(Models1(1).(names{ix});
...
values = [Models1(:).(names{ix})];
...
values = {Models1(:).(names{ix})};
Also, instead of using class and strcmp, you can just test the same conditions with isa:
v1 = Models1(1).(names{ix});
if (isa(v1, 'double') || isa(v1, 'logical'))
values = [Models1(:).(names{ix})];
% # ...
elseif (isa(v1, 'char'))
values = {Models1(:).(names{ix})};
% # ...
else
disp(['Unrecognized class: ', class(v1)]);
end
It should be much faster.