Matlab Array which stores numbers of any base

Question

This is the first Matlab code I've ever written so it's probably pretty rough.

A friend is working in Matlab and mentioned that they wanted to have an array which could take and return numbers in any base. This is what I came up with, but it doesn't work.

classdef BaseArray
   properties
      Value
   end
   methods
      function obj = BaseArray(Elements, Base)
        Value = base2dec(Elements, Base)
      end
      function add (Obj, Element, Base)
        % This might need some sort of "void" return type
        Obj.Value = [Obj.Value base2dec(Element, Base)]
      end
      function get (Obj, Base)
        % How do I get this to actually return
        str2num(dec2base(Obj.Value, Base))
   end
end

When I try to call

a=BaseArray([011, 101, 110], 2)

From the same file (this is wrong?) I get an error saying that BaseArray is not defined.

I'd like the class to work like this:

a=BaseArray([2, 4, 8], 10)
a.Add(10, 3)
a.get(2)
% returns [10, 100, 1000, 11]

Can anyone point me in the right direction?

Answer 1

You almost have it working. Let's go through a summary of the changes you need to get this fully working:

(1) You need to inherit from the handle class if you want your object to maintain its changes after you run through your methods. This can be done by appending the following to your classdef definition:

classdef BaseArray < handle

Check out a related post on why this is so: How to modify properties of a Matlab Object

(2) base2dec requires a string representation of the number. As such, you can't use an array of numbers or MATLAB is going to complain. As such, when you create an object of type BaseArray, you need to do it like this:

a = BaseArray({'2', '4', '8'}, 10);

Take note that I declared a cell array of strings. We can't throw this into a normal array, or else the strings will just concatenate with each other and it will form a single string of 248, which is obviously not what we want.

(3) When you're adding in a number, when you created your initial object, your Value property will actually be a column of numbers due to the nature of base2dec. As such, you need to concatenate the numbers vertically instead of horizontally. As such, your add method needs to be:

  function add(obj, Element, Base)
    %//This might need some sort of "void" return type
    obj.Value = [obj.Value; base2dec(Element, Base)];
  end

Also, make sure you call add this way:

a.add('3', 10);

... not a.add(10,3) as you had it before. You flipped the number and the base... you also need to ensure that 3 is a string.

(4) You missed an end statement at the end of the get method

(5) The get method is almost correct. You just have to create an output variable, and assign the call from str2num to that variable. As such:

  function val = get(obj, Base)
    %//How do I get this to actually return
    val = str2num(dec2base(obj.Value, Base));
  end

---

With all of this, this is what your final class definition looks like. Make sure you save this to a file called BaseArray.m:

classdef BaseArray < handle
   properties
      Value;
   end
   methods
      function obj = BaseArray(Elements, Base)
        obj.Value = base2dec(Elements, Base);
      end
      function add(obj, Element, Base)    
        obj.Value = [obj.Value; base2dec(Element, Base)];
      end
      function val = get(obj, Base)
        val = str2num(dec2base(obj.Value, Base));
      end
   end
end

Going with your example, we thus have:

a = BaseArray({'2', '4', '8'}, 10);
a.add('3', 10);
b = a.get(2);

b gives us:

b =

      10
     100
    1000
      11