Generic sorting of multidimensional objects

[chris34525]

Hi,

I have a class that contains four data members, i.e.,

	class ClassA
	{
		...
		private:
			int property1;
			int property2;
			int property3;
			int property4;
	};

I create a vector of these objects which I need to sort by any combination of these properties (one or more) in a generic way. For example, something like:

void sortByOneProperty(std::vector<ClassA*>& vec, ...property...);
void sortByTwoProperties(std::vector<ClassA*>& vec, ...property..., ...property...);
void sortByThreeProperties(std::vector<ClassA*>& vec, ...property..., ...property..., ...property...);
void sortByFourProperties(std::vector<ClassA*>& vec, ...property..., ...property..., ...property..., ...property...);

The solution has to be generic enough to avoid enumerating all possible combinations of sorting properties into respective "void sort...(...)" functions.

Any ideas?
Chris

[webJose]

If all properties are of the same type and the type implements operator<, you could do it by using memory pointers, a small functor and the std::sort() function.

struct Props
{
    int prop1;
    int prop2;
    int prop3;
    int prop4;
};

class ClassA
{
private:
    Props _props;
public:
    //Index is zero-based.
    bool CompareTo(int index, const ClassA &other)
    {
        //CORRECTION HERE!!!
        int &myVal = *(&_props + index);
        int &otherVal = *(&other._props + index);
        return ( myVal < otherVal);
    }
};

class CompareFunctor
{
private:
    int _propIndex;

public:
    CompareFunctor(int propIndex) : _propIndex(propIndex)
    { }
    bool operator()(const ClassA &op1, const ClassA &op2)
    {
        return op1.CompareTo(_propIndex, op2);
    }
};

.....
//Now, whenever you need to sort, you do:
typedef std::vector<ClassA> ClassACollection;
ClassACollection someCollection;
//Fill the collection up.
...
std::sort(someCollection.begin(), someCollection.end(), CompareFunctor(theIndexPropertyGoesHere));

[chris34525]

Thanks webJose. This is a pretty elegant solution!
Chris

[webJose]

NP. See the small correction I did to the code. I was comparing pointers and not the values pointed to by the pointers.

[chris34525]

Sure. Thanks a lot!
Chris