How to put together variables(matrix, vector etc..) with different type of size.

Hello, Is there any way to make variables,with different types or sizes, contained in one place.

I thought 'struct' is ok, but I need to access members with index.

'robot_state' is struct variable and have 3 fields, 'position','velocity','acceleration'.

But it cannot be accessed by index as far as I know.

For example, I cannot access 'velocity' field, with the expression like 'robot_state[2]'.

Guys, is there any way to solve this?

thank you very much.

Answer 1

[Doug]

robot_state = struct('position',{'top','bottom'}, 'velocity',{10,20}, 'acceleration',{0.1,0.3});

>> robot_state(2)

ans =

        position: 'bottom'
        velocity: 20
    acceleration: 0.3000

>> robot_state(2).velocity

ans =

    20

Answer 2

[Guillaume]

To make variables,with different types or sizes, contained in one place use a cell array.

robot_state = {'bottom', 20, 0.3};
robot_state{2}

     ans = 
         20

You can convert a structure into a cell array with struct2cell:

robot_state = struct('position', 'bottom', 'velocity', 20, 'acceleration', 0.3);
c = struct2cell(robot_state);
c{2}

     ans = 
         20

Another option is to use dynamic field names with fieldnames:

robot_state = struct('position', 'bottom', 'velocity', 20, 'acceleration', 0.3);
fn = fieldnames(robot_state);
robot_state.(fn{2})

     ans = 
         20

I'm not sure why you want to use numeric indices to access the fields of a structure, though. What's wrong with using the field name which is a lot easier to understand than an arbitrary meaningless number. robot_state.velocity is a lot clearer (i.e. less bugs) than robot_state{2}.