我有一个std::vector,其中包含许多对象,每个对象都带有与之相关联的数字组标识符。对象还具有“大小”和“名称”等属性。
我需要能够按名称、大小和其他属性对对象向量进行排序,同时保持它们在一起(例如通过上述组标识符进行分组)。
如何实现这个目标?
我需要能够按名称、大小和其他属性对对象向量进行排序,同时保持它们在一起(例如通过上述组标识符进行分组)。
如何实现这个目标?
static bool CompareWidget(const Widget& w1, const Widget& w2)
{
if(w1.GetGroupNumber() != w2.GetGroupNumber())
return (w1.GetGroupNumber() < w2.GetGroupNumber());
if(w1.GetHeight() != w2.GetHeight())
return (w1.GetHeight() < w2.GetHeight();
/// etc
return false;
}
static void SortWidgetVector(WidgetVector& widgetVector)
{
std::sort(widgetVector.begin(), widgetVector.end(), CompareWidget);
}
struct MyPredicate {
bool operator() (const MyClass& lhs, const MyClass& rhs) const {
if (lhs.groupID != rhs.groupID) {
return lhs.groupId < rhs.groupId;
} else if (lhs.name != rhs.name) {
return lhs.name < rhs.name;
else
return lhs.size < rhs.size.
}
}
};
std::sort(myObjects.begin(), myObjects.end(), MyPredicate());
将群组标识符用作主排序关键字。
例如,要按组、名称、大小排序,您可以使用比较对象,例如:
class my_comparison : public std::binary_function< object, object, bool >
{
public:
inline bool operator()(
object const &left,
object const &right ) const
{
return ( left.group_id < right.group_id ? true :
left.group_id > right.group_id ? false :
left.name < right.name ? true :
left.name > right.name ? false :
left.size < right.size );
}
};
std::sort()
函数的实例。#include <vector>
#include <iostream>
#include <algorithm>
#include <iterator>
#include <cstdlib>
template <class FirstCondition, class SecondCondition>
class by_two_criteria_t
{
FirstCondition first;
SecondCondition second;
public:
by_two_criteria_t(FirstCondition f, SecondCondition s): first(f), second(s) {}
template <class T>
bool operator()(const T& a, const T& b) const
{
return first(a, b) || (!first(b, a) && second(a, b));
}
};
template <class FirstCondition, class SecondCondition>
by_two_criteria_t<FirstCondition, SecondCondition> by_two_criteria(FirstCondition f, SecondCondition s)
{
return by_two_criteria_t<FirstCondition, SecondCondition>(f, s);
}
class X
{
int group;
int value;
public:
X(int g, int n): group(g), value(n) {}
friend bool compare_group(const X& a, const X& b);
friend bool compare_value(const X& a, const X& b);
friend std::ostream& operator<<(std::ostream& os, const X& x) { return os << x.group << ", " << x.value; }
};
bool compare_group(const X& a, const X& b) { return a.group < b.group; }
bool compare_value(const X& a, const X& b) { return a.value < b.value; }
X random_x()
{
return X(rand() % 10, rand() % 20);
}
int main()
{
using namespace std;
vector<X> vec;
generate_n(back_inserter(vec), 100, random_x);
sort(vec.begin(), vec.end(), by_two_criteria(compare_group, compare_value));
copy(vec.begin(), vec.end(), ostream_iterator<X>(cout, "\n"));
}
只是为了好玩,这里有一个函数对象,它结合了 n 个比较条件(仅适用于C++0x的可变模板和新式初始化语法):
#include <functional>
template <class T, class ...Fun>
class n_criteria_t {};
template <class T, class Fun1, class ...FunN>
class n_criteria_t<T, Fun1, FunN...>: public std::binary_function<T, T, bool>
{
public:
n_criteria_t(Fun1 f1, FunN... fn): f1(f1), f2(fn...) {}
bool operator() (const T& a, const T& b) const
{
return f1(a, b) || (!f1(b, a) && f2(a, b));
}
private:
Fun1 f1;
n_criteria_t<T, FunN...> f2;
};
template <class T, class Fun1>
class n_criteria_t<T, Fun1>: public std::binary_function<T, T, bool>
{
public:
n_criteria_t(Fun1 f1): f1(f1) {}
bool operator() (const T& a, const T& b) const
{
return f1(a, b);
}
private:
Fun1 f1;
};
template <class T, class ...Fun>
n_criteria_t<T, Fun...> n_criteria(Fun... f)
{
return {f...};
}
您可以使用partition或stable_partition将对象分成几个集合并单独对它们进行排序。我不确定它会更快还是更慢,但在我看来,代码会稍微更易于理解。
class GroupPredicate : std::unary_function<object, bool>
{
public:
GroupPredicate(INT group)
: m_group(group)
{
}
inline bool operator()(const object &object)
{
return object.group == m_group;
}
INT m_group;
};
class SizeSort : public std::binary_function<object, object, bool>
{
public:
inline bool operator()(const object &left, const object &right)
{
return left.size < right.size;
}
};
//...
std::vector<object> arVector;
for (INT i = 0; i < groupCount; ++i)
{
std::vector<object>::iterator pEndGroup = std::partition(pStartGroup, arVector.end(), GroupPredicate(i));
std::sort(pStartGroup, pEndGroup, SizeSort());
pStartGroup = pEndGroup;
}
std::map
比较器)的地方重用它们。名称是随意的,这正是因为没有足够的输入信息来想出一个好的名称 :) - Pavel Minaevstruct
,从而有效地创建一个本地函数。 - Frerich Raabe