MATLAB: Do I get the error “Subscripted assignment dimension mismatch” when using a cell array in a structure field

Question

I have the following lines of code which work: 

layers(1)=struct('test', 'ABC', 'value', 0.50); 
layers(2)=struct('test', 'DEF', 'value', []);

I would like to combine the "test" and "value" fields into a single field like this: 

layers(1)=struct('test', {'ABC', 0.50}); 
layers(2)=struct('test', {'DEF'});

This gives the error message "Subscripted assignment dimension mismatch." 

Is there a way to put a 1×2 cell into a single field in the structure? 

Answer 1

You are getting a "Subscripted assignment dimension mismatch" error because MATLAB is using a syntax where you use a cell array to specify each of the fields in a structure array. For example, the following code creates a 1x2 struct array:

a = struct('test', {1, 2};)

You receive an error in your code occurs because you are specifying a scalar structure with the left hand syntax "layers(1)". 

The workaround is to add the cell array to the structure using the dot-notation for any entries that you would like to have variable-length cell arrays.Here is an example:

a = struct('singlevalue', 3);
a.multivalue = {1, 2};

Another workaround is to use a nested cell array. Please see the following:

a (1) = struct('singlevalue', 3, 'multivalue', {{1,2}});

In the documentation page for "struct", you can see a description of how MATLAB structs interpret a cell array parameter. Please refer to the second syntax description (s = struct(<https://www.mathworks.com/help/matlab/ref/struct.html#inputarg_field field>,<https://www.mathworks.com/help/matlab/ref/struct.html#inputarg_value value>)) at the following link:

https://www.mathworks.com/help/matlab/ref/struct.html