MATLAB: Substruct array disappear when a struc object is assigned

Question

Hi guys,

I have started to use struct to create nested arrays which will be assigned in a second time , for example:

   S = struct( ... 
  'A',               struct( ... 
  'A_ID',            struct( ...
  'C', [], ...
  'D', [], ...
  'E',               struct( ... 
  'EF',[], ... 
  'EG',[], ...
  'EH',[], ... 
  'EI',[]))));

but when i try to assign the object values, something strange happens, the substructure information disappeares. For examples i assign to the first postion of the object A_ID the value of C = 'test1'

S.A.A_ID(1).C='test1'

and i obtain

S.A.A_ID(1) =

• C: 'test1'
• D: []
• E: [1×1 struct]

now if i assign a new value for C in a new position of A_ID for example

S.A.A_ID(2).C='test2'

i don't obtain

S.A.A_ID(2) =

• C: 'test2'
• D: []
• E: [1×1 struct]

but

S.A.A_ID(2) =

• C: 'test2'
• D: []
• E: []

and i lost all the information contained in the nested struct E !!

i don't really understand why, have someone an idea??

thank's in advance

Luca

Answer 1

Luca - the substructure (for the second element) doesn't disappear as it was never there to begin with. Since you are initializing it for the first time with

 S.A.A_ID(2).C='test2';

then the D and E will be set with default values of the empty matrix for each. You would need to copy the elements over from S.A.A_ID(1).

Remember, when you initialize your S as above, then

 numel(S.A.A_ID)

is just one. There is no second element, and S.A.A_ID is identical/equivalent to S.A.A_ID(1).