Function with input an array of classes.

Maybe it's because I have a lot of programming experience in C/C++, but I am trying to build a function inside a class that takes a whole array of classes as an input. Matlab always returns "too many arguments". This is how I tried to do it.

classdef agent
  properties
    r
    v
    id
  end

    methods
      function y=mean_distance(a)
        S=sum(norm(a.r-this.r));
        y=S/(size(a)-1)
        %I also need a random access iterator to a, like disp(a(i).r(1));
      end
    end

Thanks. EDIT: class should probably have a handle for this to work, but I am unfamiliar with handles. Reading some relative tutorials.

Answer 1

[Andrew Newell]

I can't run your code because there are a lot of undefined terms, but I can see two problems. First, if you run

a(2).view(a(2),a)

it's like having 3 arguments. You should call your function using one of these two equivalent forms:

view(a(2),a)
a(2).view(a) % The a(2) is considered the first argument

Second,

n=size(agents)

will give you a vector [1 10], which will give you an error when you get to the loop

for i=1:n
  ...

Do you know how to use the debugger?

Answer 2

[Andrew Newell]

To set values in this object, you must have a class constructor. Now suppose a is an array of length 2 with a.r having values 1 and 2. Then if you type

a.r

You'll get something like this:

ans = 
     1

ans =
     2

It's a comma-separated list, not a vector. To bundle them together, you'll need square brackets, like this:

      function y=mean_distance(a,this)
        y=mean(norm([a.r]-[this.r]));
      end

A handle is not necessary for this problem.

EDIT: By the way, I substituted mean for your method, but maybe you have some reason for dividing by length(a)-1 instead of length(a)?

Answer 3

[Philip Borghesani]

You have two common mistakes here:

1. MATLAB class methods require an explicit this input
2. obj.prop returns a comma separated list that must be concatenated to use as a vector input.

Fixed Example

 classdef agent
  properties
    r
    v
    id
  end
    methods
      function y=mean_distance(this,a)
        S=sum(norm([a.r]-[this.r]));
        y=S/(numel(a)-1);
        %I also need a random access iterator to a, like disp(a(i).r(1));
      end
    end
end

A handle class is not needed for your example often simple small classes that are placed in vectors are better off as value classes.

Usage:

a=agent
a(1).r=5
a(2).r=5
b=a
b(2).r=10
mean_distance(a,b) 
% or
a.mean_distance(b)

Answer 4

[Eleftherios Ioannidis]

This worked for this function. But in another function, I did everything you said (constructors, []brackets, explicit 'this') and I still get "too many arguments". Here is the function. The class properties are the same:

   function agnts=view(this,agents)
        %search for visible agents
            constants;
            n=size(agents)
            xproduct1=0;
            xproduct2=0;
            agnts=[];
            k=1;
            for j=-J:dang:J
                vseek=([cos(j) -sin(j);sin(j) cos(j)]*[this.v]')';
                for i=1:n
                    xproduct2=det([vseek ; [agents(i).r]]);
                    if(xproduct2*xproduct1<0)
                        agnts(k)=i;
                        k=k+1;
                    end
                    xproduct1=xproduct2;
                end
            end
        end

agents: an array of type agent(self class type) agnts: a uint8 vector. constants: everything not declared here is in constants.m.

Thanks for the immediate responce.

EDIT: I call it this way:

>>for i=1:10
a(i)=agent(i); %i==id
end
>>a(2).view(a(2),a);
Error: "too many input arguments"
%the same when I run: a(2).view(a); OR a(2).view([a]);

Answer 5

[Eleftherios Ioannidis]

Thanks Andrew, with your advice I managed to fix this. And Phillip too, the [] brackets saved me. It works fine now.