Does MATLAB have a way to create a dynamic Object storing array?

I have a large number of a single type of Object, which has a few properties such as a unique ID. I need a way to store these objects in an array-like structure.

The problem is that in my script, these objects are constantly being deleted, and new Objects constantly being created.

I want a way to store my objects in such a way that they can be looked up with an integer ID, but I don't want to have to keep track of empty array spaces (which would come about if when Objects are deleted).

Basically, I'm looking for the equivalent of an ArrayList (google search may help). I've looked at containers.Map Objects, but they don't let me edit the Object Properties or call Object Methods directly from the container.

Does anyone know if such a thing exists in MATLAB?

Answer 1

[Abhipsa]

Hello @Jeremy Simpson,

I understand that you are looking for a dynamic, array-like structure in MATLAB to store and access objects by integer ID without managing empty slots, and with support for direct property/method access.

You can follow the below steps to achieve the desired behaviour in MATLAB:

1. Create a handle class: Define a custom class that inherits from handle, so objects are modified by reference.
2. Store in “containers.Map”: Use a “containers.Map”with integer keys and handle objects as values to store and retrieve objects by unique ID.
3. Access via temporary variable: Since “containers.Map” doesn't support chained indexing, first assign the object to a temporary variable before accessing or modifying its properties.
4. Changes persist: Because the objects are handles, any changes made via the temporary variable (like modifying a property or calling a method) will persist in the map.

The below code snippet demonstrates a handle class:

classdef MyObject < handle
    properties
        ID
        Value
    end
    methods
        function obj = MyObject(id, val)
            obj.ID = id;
            obj.Value = val;
        end
        function displayInfo(obj)
            disp(['ID: ' num2str(obj.ID) ', Value: ' num2str(obj.Value)]);
        end
    end
end

The properties of the class can be modified using container as below:

% Create Map
objMap = containers.Map('KeyType','int32','ValueType','any');

% Add object
obj1 = MyObject(1, 42);
objMap(obj1.ID) = obj1;

tempObj = objMap(1);    % Get the handle object
tempObj.Value = 100;    % Modify property
remove(objMap, obj1.ID); %delete the object

I hope this helps you.

[Walter Roberson]

These days, you should also consider using a dictionary instead of a containers.Map