How to create struct from fieldnames and values cell arrays for code generation ?

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Hi,
I am trying to make a "code generation friendly" function:
[output_struct] = declareStruct(list_fields, list_values)
that creates a structure knowing its fieldnames and their associated values.
The goal is to use this function in Simulink, through a Matlab system block, simulated using code generation.
None of the approches described in How to create a struct from a cell array of fieldnames and a cell array of values? - MATLAB Answers - MATLAB Central (mathworks.com) work since code generation does not support cell2struct or transpose for cell arrays.
Is there a way to create a struct this way in MATLAB R2021b, or is it only possible to explicitely declare my struct in a hardcoded fashion ?
Thanks !
Guillaume.
  3 Comments
Guillaume Dupré
Guillaume Dupré on 23 Feb 2024
Edited: Guillaume Dupré on 23 Feb 2024
The values of my fields do not have the same size.
Here is an example of what I would like to do:
list_fields = {'a'; 'b'; 'c'; 'd'}; % the function fieldnames() returns a column vector in my case
list_values = {1; [2,3,4]; 5; 6};
args = [list_fields'; list_values'];
output_struct = struct(args{:});
which returns:
struct('a', 1, ...
'b', [2 3 4], ...
'c', 5, ...
'd', 6);
However, I cannot create the args variable in a code generation context.
This is needed here to respect the syntax struct(field1, value1, field2, value2, etc...).
Stephen23
Stephen23 on 23 Feb 2024
"I cannot create the args variable in a code generation context."
Perhaps one of these would work:
  • RESHAPE()
  • create two new cells arrays with the required size, transfer the content:

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Accepted Answer

Guillaume Dupré
Guillaume Dupré on 23 Feb 2024
Edited: Guillaume Dupré on 23 Feb 2024
Hi all,
Based on Stephen23 and Matt J advices, I managed to produce the following solution:
list_fields = {'a'; 'b'; 'c'; 'd'}; % the function fieldnames() returns a column vector in my case
list_values = {1; [2,3,4]; 5; 6};
% For loop to cast list_fields and list_values in another cell without
% transpose or concatenate
num_fields = length(list_fields);
args = cell(2,num_fields);
for i = 1:num_fields
args{1,i} = list_fields{i};
args{2,i} = list_values{i};
end
output_struct = struct(args{:})
Thank you for your help !

More Answers (1)

Matt J
Matt J on 23 Feb 2024
Edited: Matt J on 23 Feb 2024
Does it support transpose for normal arrays? If so, then you might be able to do,
list_fields = {'a'; 'b'; 'c'; 'd'}; % the function fieldnames() returns a column vector in my case
list_values = {1; [2,3,4]; 5; 6};
args = [list_fields, list_values];
idx=reshape(1:numel(args),size(args))';
output_struct = struct(args{idx(:)})
output_struct = struct with fields:
a: 1 b: [2 3 4] c: 5 d: 6
  1 Comment
Guillaume Dupré
Guillaume Dupré on 23 Feb 2024
Edited: Guillaume Dupré on 23 Feb 2024
Thank you for your answer.
I tried it but unfortunately code generation does not support concatenation of cell arrays.
I will try to combine it with the 2nd solution of Stephen23 to see if this works.

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