Does MATLAB have any set-like datatype?

Question

I am looking for a way to compare finite sequential data with non-deterministic ordering in MATLAB. Basically, what I want is an array, but without imposing an order on the contained elements. If I have the objects

a = [x y z];

and

b = [x z y];

I'd want isequal(a, b) to return true. With arrays, this is not the case. The easy fix would be to sort the entries before comparing them. Unfortunately, in my case the elements are complex objects which cannot easily be mapped to have an unambigious numerical relationship to each other. Another approach would be not to use isequal , but rather a custom comparison function which asserts matching lengths and then simply checks if each element from the first array is contained in the second one. However, in my case the arrays are non-trivially nested inside the structs I am trying to compare via isequal , and it would be quite complicated to write a custom comparison function for the encapsulating structs. Other than this ordering problem, the inbuilt isequal function covers all of my needs, as it correctly handles arbitrarily nested structs with arbitrary fields, so I would really like to avoid writing a complicated custom function for that.

Is there any datatype in MATLAB which allows for the described behavior? Or is there a way to easily build such a custom type? In Java, I could simply write a wrapper class with a custom implementation for the equals method, but there seems to be no such mechanism in MATLAB?

Answer 1

I've found a way to solve my problem elegantly. Contrary to my previously stated belief, MATLAB actually does allow for class-specific overriding of isequal .

classdef CustomType
    properties
        value
    end

    methods
        function self = CustomType(value)
            self.value = value;
        end

        function equal = isequal(self, other)
            if not(isa(other, 'CustomType'))
                equal = false;
                return;
            end

            % implement custom comparison rules here
        end
    end
end

So, I can simply assign the fields in question like this and don't have to change anything else in my code:

a = Set([x y z]); % custom type
...
b = Set([x z y]);
...
isequal(a, b); % true

In my use case, I don't even need the uniqueness property of sets. So I only have to perform order-independent comparison and don't need to waste performance on ensuring unrequired properties. Furthermore, by using a dedicated type, I can differentiate explicitly between fields which have order (ie regular arrays) and those which don't, at the moment of assignment.

Another solution might be to overwrite the inbuilt isequal and make it apply custom comparison rules when its arguments are of specific type. However, this would slow down all comparisons in the whole program and make for bad encapsulation. I feel like using a custom type with an overriden isequal is the way to solve this kind of problem. But I still think that sets (and other types of commonly used containers) should be included in the basic repertoire of MATLAB.