After reading your answer and thinking a bit I've got this code to work:

static bool CompareGetDistances(Value &a, Value &b)
{
	return a[5] < b[5];
}
...
    ValueArray &rows = SomeValuaArrayOfValueMap();
    Vector<Value> &vv = const_cast< Vector<Value>& >(rows.Get());
    Sort(vv, CompareGetDistances);
...

Thanks for your help !

	Vector<Value> v = clone(va.Get());
	Sort(v);
	va = ValueArray(pick(v));