How do I access a field on a struct which is not always in the same level?

Hello,

I have a problem in generalizing a code for different structure contents. The problem is that I need to access a field (let's say subfield1) which is not always in the same level of the structure.

var1.subfield1 = 1;
var2.field1.subfield1 = 3;

I would like to be able to define a variable, fieldname, that would be empty for var1 and 'field1' for var2, so that:

var1.(fieldname).subfield1
var2.(fieldname).subfield1

would work and give me the value of that field. However if I set:

fieldname=''

and try to execute the first line, this gives an error:

Reference to non-existent field ''.

I have also tried using the getfield function, with no success.

Is there any solution for this, or should the structures have the same fields from the beginning to be able to do this?

Thank you very much in advance,

Ana Gómez

[Ameer Hamza]

What about treating this as a special case and adding an if statement.

if ~isempty(fieldname)
  var1.(fieldname).subfield1
else
  var1.subfield1
end

[Ana]

Yes, that would be one option.

The problem is that I am using this quite often in the code so it would be more recommendable if I could avoid filling it of "if" statements if there is the possibility.

Thanks in any case for the suggestion.

[KSSV]

Why don't you create some dummy filedname.....this dummy filedname will be already known to you....

var1.dummy.subfield1 = 1;
var2.field1.subfield1 = 3;

Answer 1

[Jan]

Create a function which checks the existence of the subfield:

function Data = getSubField(S, F1, F2)
if isfield(S, F2)
  Data = S.(F2);
elseif isfield(S, F1)
  Data = S.(F1).(F2);
else
  Data = [];
end

Now call this like:

var1.subfield1 = 1;
var2.field1.subfield1 = 3;
Data1 = getSubField(var1, 'field1', 'subfield1');
Data2 = getSubField(var2, 'field1', 'subfield1');

If run-time matters, this might be faster - or slower (try it by your own):

function Data = getSubField(S, F1, F2)
try
  Data = S.(F2);
catch
  try
    Data = S.(F1).(F2);
  catch
    Data = [];
  end
end

[Ana]

Perfect! Thank you very much for the answer.

Answer 2

[Stephen23]

This is easy with getfield, you just need to define a cell array of the required fieldnames:

>> var1.subfield1 = 1;
>> var2.field1.subfield1 = 3;
>> c1 = {'subfield1'};
>> c2 = {'field1','subfield1'};
>> getfield(var1,c1{:})
ans =  1
>> getfield(var2,c2{:})
ans =  3

[Ana]

Thanks for the answer! In the use I was making in my code, having a function was more appropriate, so I finally used Jan's answer, but this is also very useful for some other problems I may face in the future.