Multiple numerics as one map key / Merge Objects based on parameters

I want to use two numerics as a single key for a map to merge similar objects of a class. How can I do that?

My class looks like this:

classdef Foo
    properties
        a double
        b double
        val double
    end
    
    methods
        function obj = Foo(a,b,val)
            obj.a   = a;
            obj.b   = b;
            obj.val = val;
        end
        
        function o = plus(l,r)
            o = Foo(l.a,l.b,l.val+r.val);
        end
        
        function k = getKey(obj)
            <...>
        end
    end
end

The code should do the following:

fooCell = {Foo(3,4,100) Foo(3,4,20) Foo(2,5,20)};
fooMap  = containers.Map('KeyType', <...> ,'ValueType','any');
for i=1:length(fooCell)
    k = fooCell{i}.getKey;
    if fooMap.isKey(k)
        fooMap(k) = fooMap(k)+fooCell{i};
    else
        fooMap(k) = fooCell{i};
    end
end
fooMap.values %Should contain 2 objects: Foo(3,4,120) & Foo(2,5,20)

How should the getKey method look like?

Answer 1

[Jan Siegmund]

The only keytype which can hold two doubles is the character key type. So one may use char as key type and then simply

function k = getKey(obj)
    k = num2str([obj.a obj.b],'%d');
end

An even faster approach could be

function k = getKey(obj)
    k = char(typecast([obj.a obj.b],'uint16'));
end

As every char in MATLAB is 16bit. This may produce non-printable keys though.