Error using a structure array in a for loop.

Hello,

When I use the structure array ('new_popc.Position') in a loop I get the following error after the second iteration:

'Scalar structure required for this assignment.'
'Error in TEST (line 19)'
		'new_popc.Position = repmat(empty_individual, length(pop_unique), 2);'

This is the code:

count = 0;
for k = 1:5		
    pop_unique = zeros(100, 2);
    count = count + 1

    % RESHAPE POPULATION
     for i = 1:100 
	     pop_unique(i,:) = out.pop(i).Position;
     end
    [pop_unique, ia, ic] = unique(pop_unique, 'first','rows');

    %% CREATE A NEW STRUCTURE WITH THE NEW ARRAY
	empty_individual = [];
	new_popc.Position = repmat(empty_individual, length(pop_unique), 2);
        
 	for j = 1:length(pop_unique)
 	    new_popc(j).Position = pop_unique(j,:);
    end
[out.pop.Position] = new_popc.Position;
        
end

I think it must be to when I update the structure array. How can I fix this error?

Thanks in advance.

Answer 1

[Walter Roberson]

[out.pop.Position] = new_popc.Position;

That is an error if out is a non-scalar struct. If out is a non-scalar struct then out.pop would be struct expansion, and when you use struct expansion you cannot use a substructure reference in the assignment.

Be careful, the right hand side involves the non-scalar struct new_popc so new_popc.position generates multiple outputs.

If out did not exist before the assignment, or if it were a scalar struct that did not have a field named pop, or if it were a scalar struct with a non-scalar struct the same number of elements as new_popc, then in any of those three cases, the assignment you wrote would be valid, and would copy the position information from new_popc to out.pop .

[Yro]

Thanks for your comments.

The problem is from iteration 1 when the array already exists, for this first iteration if it works what I want to do. What I am doing is to eliminate the repeated values of the array out.pop.Position, for with the unique function, I create the array new_pop.Position and then with this array I update out.pop.Position. But this only works for the first iteration, and in the second it does not work because the array new_pop.Position exists. How could I update this array to not get this error, or some other way to assign the pop_unique array to out.pop.Position.