Question

Is it possible to iterate through a MATLAB structure numerically like a vector instead of using the field names?

Simply, I am trying to do the following inside an EML block for Simulink:

S.a.type = 1;
S.a.val = 100;
S.a.somevar = 123;    
S.b.type = 2;
S.b.val = 200;
S.b.somevar2 = 234;
S.c.type = 3;
S.c.val = 300;
S.c.somevar3 = 345;

for i = 1:length(s)
    itemType = S(i).type;
    switch itemType
        case 1
            val = S(i).val * S(i).somevar1;
        case 2
            val = S(i).val * S(i).somevar2;
        case 3
            val = S(i).val * S(i).somevar3;
        otherwise
            val = 0
    end
end

disp(var);

Answer 1

You need to use the field names, but you can do so dynamically. If you have a structure defined as:

s.field1 = 'foo';
s.field2 = 'bar';

Then you can access the field field1 with either

s.field1
s.('field1')

The only thing you need is the function fieldnames to dynamically get the field names such that your code example will look somewhat like

elements = fieldnames(S);
for iElement = 1:numel(elements)
   element = S.(elements{iElement});
   itemType = element.type;
   switch itemType
      case 1
          val = element.val * element.somevar1;
      case 2
          val = element.val * element.somevar2;
      case 3
          val = element.val * element.somevar3;

   end
end

If those are the exact field names, you should do some other things. First of all you would need to rethink your names and secondly you could use part of Matt’s solution to simplify your code.