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Structures in MATLAB

In this tutorial we will explain what MATLAB structures are and how to work with them.

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Create a Simple Structure

A structure is a data type that groups related data using named fields.

You can create one using direct assignment or with the struct function.

robot.name      = 'MyRobot';
robot.DOF       = 6;
robot.payload   = 2.5           

robot = struct with fields:
       name: 'MyRobot'
        DOF: 6
    payload: 2.5000

Equivalent creation with struct()

robot2 = struct('name','MyRobot', ...
    'DOF',6, ...
    'payload',2.5)

robot2 = struct with fields:
       name: 'MyRobot'
        DOF: 6
    payload: 2.5000

Nested Structures

Structures can contain other structures, enabling hierarchical data.

robot2.links(1) = struct('length',0.5,'mass',4.0)

robot2 = struct with fields:
       name: 'MyRobot'
        DOF: 6
    payload: 2.5000
      links: [1x1 struct]

robot2.links(2) = struct('length',0.4,'mass',3.5)

robot2 = struct with fields:
       name: 'MyRobot'
        DOF: 6
    payload: 2.5000
      links: [1x2 struct]

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Accessing Fields

Fields are accessed with dot notation: StructureName.FieldName

Read a field

robotName=robot.name

robotName = 'MyRobot'

Write/update a field

robot.payload = 3.0

robot = struct with fields:
       name: 'MyRobot'
        DOF: 6
    payload: 3

Access nested field

link1_length = robot2.links(1).length

link1_length = 0.5000

robot2.links(2).length = 0.8;

Dynamic Field Names

You can add or access fields with variable names using parentheses.

newfield = 'maxSpeed';
robot.(newfield) = 1.2;               % adds a new field maxSpeed

Check existence before access

if isfield(robot, newfield)
    RobotMaxSpeed = robot.maxSpeed
end

RobotMaxSpeed = 1.2000

Adding and Removing Fields

Use setfield and rmfield, or direct manipulation.

Add a field

robot = setfield(robot, 'manufacturer', 'UniversalRobots')

robot = struct with fields:
            name: 'MyRobot'
             DOF: 6
         payload: 3
        maxSpeed: 1.2000
    manufacturer: 'UniversalRobots'

Remove a field

robot = rmfield(robot, 'manufacturer')

robot = struct with fields:
        name: 'MyRobot'
         DOF: 6
     payload: 3
    maxSpeed: 1.2000