How to Use sort to Sort an Array of Custom Class Objects in MATLAB？

I have already overloaded the eq, lt, and gt methods in my class definition, but I am still encountering an issue when trying to sort using the sort function.

error sort

Incorrect number or types of inputs or outputs for function sort.

[Ayush Modi]

Hi Jia, Could you provide the code for us to check the issue ?

[jia]

classdef PointGroupElement
    % POINTGROUPELEMENT is an element of a point group
    %
    % Parameters
    % ------
    % R : Real space rotation action of the operator. Square matrix with
    % size of the number of spatial demension.
    % conjugate : boolean (default false)
    properties
        R;
        conjugate;
        antisymmetry;
        U;
    end

    methods
        function obj = PointGroupElement(R,options)
            arguments
                R           (:,:) double;
                options.conjugate (1,1) logical  = false;
                options.antisymmetry (1,1) logical  = false;
                options.U (:,:)  = [];
            end
            [obj.R,obj.conjugate,obj.antisymmetry,obj.U] = deal(real(R),options.conjugate,options.antisymmetry,options.U);
        end
               function eq_g = eq(obj,g)
            arguments
                obj ;
                g   ;
            end
            eq_g = arrayfun(@(x) eq_(x,g),obj);
            function eq_AB = eq_(A,B)
                R_eq = norm(A.R-B.R)<1e-5;
                basic_eq = R_eq && (A.antisymmetry==B.antisymmetry) && (A.conjugate==B.conjugate);
                U_eq = norm(A.U-B.U)<1e-5;
                eq_AB = U_eq && basic_eq;
            end
        end
        function result = lt(obj,g)
            result = arrayfun(@(x) lt_(x,g),obj);
            function result_ = lt_(A,B)
                if ~isequal([A.conjugate,A.antisymmetry],[B.conjugate,B.antisymmetry])
                    if A.conjugate<B.conjugate
                        result_ = true;
                    elseif (A.antisymmetry < B.antisymmetry) && A.conjugate==B.conjugate
                        result_ = true;
                    else
                        result_ = false;
                    end
                else
                    result_ = string(char(reshape(A.R,1,[])))<string(char(reshape(B.R,1,[])));
                end
            end
        end

        function result = gt(obj,g)
            result = ~(eq(obj,g) + lt(obj,g));
        end
    end
end

R1 = eye(3);
g = PointGroupElement(R1);
R2 = -R1;
g1 = PointGroupElement(R2);
g1<g2 % 0
g1>g2 % 1
g1==g2 % 0
sort([g1,g2]) 
% Error using sort
% Incorrect number or types of inputs or outputs for function sort.

[Stephen23]

"I have already overloaded the eq, lt, and gt methods in my class definition"

Why? AFAIK SORT does not use them.

Just define a SORT method.

Answer 1

[Divyam]

Hi Jia, ensure that your custom class is defined in a ".m" file with name as the class name. "MyClass.m" has been attached as the reference class for the code below.

To test sorting, the following code was created in a different MATLAB file in the same directory where the class was defined.

% Creating an array of custom class objects
array = [MyClass(5), MyClass(2), MyClass(8), MyClass(3)];

% Extracting the "Value" of the objects in an array using the arrayfun method
valuesExtract = arrayfun(@(obj) obj.Value, array);

% Sorting the values to get the sorted indices
[~, sortedIndices] = sort(valuesExtract);

% Reorder the array based on the sorted indices
sortedArray = array(sortedIndices);

% Displaying the sorted values
for i = 1:length(sortedArray)
    fprintf("%d ", sortedArray(i).Value);
end

2 3 5 8 

The issue might be caused by not using "arrayfun" to extract the "Value" property which has to be compared and comparing the property directly.

For more information regarding the use of "arrayfun" method refer to the following documentation: https://www.mathworks.com/help/matlab/ref/arrayfun.html