C# 如何为独立于对象顺序的对象集合生成唯一哈希
假设我有一节课C# 如何为独立于对象顺序的对象集合生成唯一哈希,c#,.net,collections,equality,gethashcode,C#,.net,Collections,Equality,Gethashcode,假设我有一节课 public class MyClass { public string Type { get; set; } public int Id { get; set; } } 我有一个集合类,它只是一个强类型列表 public class MyClassList : List<MyClass> { public MyClassList(IEnumerable<MyClass> enumerable) : base (enumerabl
public class MyClass
{
public string Type { get; set; }
public int Id { get; set; }
}
我有一个集合类,它只是一个强类型列表
public class MyClassList : List<MyClass>
{
public MyClassList(IEnumerable<MyClass> enumerable) : base (enumerable) {}
}
公共类MyClassList:List
{
公共MyClassList(IEnumerable可枚举):基(可枚举){}
}
我希望MyClassList
能够基于内容为MyClassList
生成唯一的哈希代码。MyClass
的哈希代码应基于这两个属性即使对象的顺序不同,MyClassList
的哈希代码也应该相同
为了处理排序问题,我想我可以在生成哈希代码之前对列表进行排序,但我不确定如何生成列表的哈希代码。我提出了这个解决方案(我没有实现Equals方法):
公共类MyClass
{
公共字符串类型{get;set;}
公共int Id{get;set;}
公共覆盖int GetHashCode()
{
int hash=17;
hash=hash+23*this.Type.GetHashCode();
hash=hash+23*this.Id.GetHashCode();
返回散列;
}
}
公共类MyClassList:List
{
公共MyClassList(IEnumerable可枚举):基(可枚举){}
公共覆盖int GetHashCode()
{
返回这个.Aggregate(17,(state,current)=>state*23+current.GetHashCode());
}
}
生成hashcode的方法受Microsoft计算匿名对象的哈希值的方法启发。clto给出的解决方案有效。这里有一种替代方法:按总排序对列表进行排序(只要不含糊,任何排序都可以)。然后可以使用任何常规方法计算哈希代码。你不需要秩序独立。您甚至可以使用加密哈希函数。如果顺序不重要,那么您应该使用本质上是集合的集合,而不是列表 此外,通常最好不要从集合继承;用构图代替 因此,对于集合,可以使用
HashSet
,因为它具有set语义
要让MyClass
使用这两个属性作为它的标识,只需重写它的equals并获得哈希代码实现,或者创建一个IComparer
,如果您不能或不想这样做的话
public class MyClass:IEquatable<MyClass>
{
public string Type { get; set; }
public int Id { get; set; }
public override bool Equals(object obj)
{
return Equals(obj as MyClass);
}
public bool Equals(MyClass other)
{
if (other == null)
return false;
return Type == other.Type &&
Id == other.Id;
}
public override int GetHashCode()
{
return Type.GetHashCode() * 79 + Id;
}
}
公共类MyClass:IEquatable
{
公共字符串类型{get;set;}
公共int Id{get;set;}
公共覆盖布尔等于(对象对象对象)
{
返回等于(obj作为MyClass);
}
公共布尔等于(MyClass其他)
{
如果(其他==null)
返回false;
返回类型==其他.Type&&
Id==other.Id;
}
公共覆盖int GetHashCode()
{
返回类型.GetHashCode()*79+Id;
}
}
那么您的收藏就简单到:
HashSet<MyClass> set = new HashSet<MyClass>();
HashSet=newhashset();
如果您想比较不同的集合,只需使用:
HashSet<MyClass>.CreateSetComparer();
HashSet.CreateSetComparer();
为了获得最佳性能,我会尽量避免每次调用GetHashCode
时重复整个集合。GetHashCode
的目的是将性能提高到比评估每个元素更好的程度。因此,当列表中的元素发生如下更改时,我可能会尝试维护哈希代码
class Program
{
static void Main(string[] args)
{
MyClassList l = new MyClassList() { new MyClass() {Type="Bob", Id=1}, new MyClass() {Type="Jones", Id=2}};
MyClassList l2 = new MyClassList() { new MyClass() { Type = "Jones", Id = 2 }, new MyClass() { Type = "Bob", Id = 1 } };
MyClassList l3 = new MyClassList() { new MyClass() { Type = "Jones", Id = 2 }};
Console.WriteLine("{0} {1} {2}", l.GetHashCode(), l2.GetHashCode(), l3.GetHashCode());
l3.Add(new MyClass() { Type = "Bob", Id = 1 });
Console.WriteLine("{0}", l3.GetHashCode());
}
}
public class MyClass
{
public string Type { get; set; }
public int Id { get; set; }
public override int GetHashCode()
{
return (Type.GetHashCode() % 0x8000) | (int)((uint)Id.GetHashCode() & 0xFFFF0000);
}
}
public class MyClassList : IList<MyClass>
{
List<MyClass> internalList;
int hashCode = 0;
public MyClassList()
{
internalList = new List<MyClass>();
}
private void IncludeInHash(MyClass item)
{
hashCode ^= item.GetHashCode();
}
private void ExcludeFromHash(MyClass item)
{
IncludeInHash(item);
}
public override int GetHashCode()
{
return hashCode;
}
public int IndexOf(MyClass item)
{
return internalList.IndexOf(item);
}
public void Insert(int index, MyClass item)
{
internalList.Insert(index, item);
// Make sure Insert is successful (doesn't throw an exception) before affecting the hash
IncludeInHash(item);
}
public void RemoveAt(int index)
{
MyClass reduce = internalList[index];
internalList.RemoveAt(index);
// Make sure RemoveAt is successful before affecting the hash
ExcludeFromHash(reduce);
}
public MyClass this[int index]
{
get
{
return internalList[index];
}
set
{
MyClass reduce = internalList[index];
internalList[index] = value;
// Make sure these happen atomically; don't allow exceptions to prevent these from being accurate.
ExcludeFromHash(reduce);
IncludeInHash(value);
}
}
public void Add(MyClass item)
{
internalList.Add(item);
IncludeInHash(item);
}
public void Clear()
{
internalList.Clear();
hashCode = 0;
}
public bool Contains(MyClass item)
{
return internalList.Contains(item);
}
public void CopyTo(MyClass[] array, int arrayIndex)
{
internalList.CopyTo(array, arrayIndex);
}
public int Count
{
get { return internalList.Count; }
}
public bool IsReadOnly
{
get { return false; }
}
public bool Remove(MyClass item)
{
if (internalList.Remove(item))
{
ExcludeFromHash(item);
return true;
}
else
return false;
}
public IEnumerator<MyClass> GetEnumerator()
{
return internalList.AsReadOnly().GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
类程序
{
静态void Main(字符串[]参数)
{
MyClassList l=newmyclasslist(){newmyclass(){Type=“Bob”,Id=1},newmyclass(){Type=“Jones”,Id=2};
MyClassList l2=new MyClassList(){new MyClass(){Type=“Jones”,Id=2},new MyClass(){Type=“Bob”,Id=1};
MyClassList l3=new MyClassList(){new MyClass(){Type=“Jones”,Id=2};
WriteLine(“{0}{1}{2}”,l.GetHashCode(),l2.GetHashCode(),l3.GetHashCode());
添加(newmyclass(){Type=“Bob”,Id=1});
WriteLine(“{0}”,l3.GetHashCode());
}
}
公共类MyClass
{
公共字符串类型{get;set;}
公共int Id{get;set;}
公共覆盖int GetHashCode()
{
返回(Type.GetHashCode()%0x8000)|(int)((uint)Id.GetHashCode()&0xFFFF0000);
}
}
公共类MyClassList:IList
{
名单;
int hashCode=0;
公共MyClassList()
{
internalList=新列表();
}
私有void IncludeInHash(MyClass项目)
{
hashCode^=item.GetHashCode();
}
私有void ExcludeFromHash(MyClass项)
{
IncludeInHash(项目);
}
公共覆盖int GetHashCode()
{
返回哈希码;
}
public int IndexOf(MyClass项)
{
返回internalList.IndexOf(项目);
}
公共void插入(int索引,MyClass项)
{
内部列表。插入(索引,项目);
//在影响哈希之前,确保插入成功(不引发异常)
IncludeInHash(项目);
}
公共无效删除(整数索引)
{
MyClass reduce=内部列表[索引];
internalList.RemoveAt(索引);
//在影响哈希之前,请确保RemoveAt成功
ExcludeFromHash(reduce);
}
公共MyClass此[int索引]
{
得到
{
返回内部列表[索引];
}
设置
{
MyClass reduce=内部列表[索引];
内部列表[索引]=值;
//确保这些事件以原子方式发生;不要允许异常来阻止这些事件的准确性。
ExcludeFromHash(reduce);
IncludeInHash(值);
}
}
公共作废添加(MyClass项目)
{
内部列表。添加(项目);
IncludeInHash(项目);
}
公共空间清除()
{
internalList.Clear();
hashCode=0;
}
公共布尔包含(MyClass项)
{
返回内部列表。包含(项);
}
public void CopyTo(MyClass[]数组,int arrayIndex)
{
CopyTo(数组,arrayIndex);
}
公共整数计数
{
获取{return internalList.Count;}
}
公共图书馆是只读的
{
获取{return false;}
}
公共布尔删除(MyClass项)
{
如果(内部列表。删除(项目))
class Program
{
static void Main(string[] args)
{
MyClassList l = new MyClassList() { new MyClass() {Type="Bob", Id=1}, new MyClass() {Type="Jones", Id=2}};
MyClassList l2 = new MyClassList() { new MyClass() { Type = "Jones", Id = 2 }, new MyClass() { Type = "Bob", Id = 1 } };
MyClassList l3 = new MyClassList() { new MyClass() { Type = "Jones", Id = 2 }};
Console.WriteLine("{0} {1} {2}", l.GetHashCode(), l2.GetHashCode(), l3.GetHashCode());
l3.Add(new MyClass() { Type = "Bob", Id = 1 });
Console.WriteLine("{0}", l3.GetHashCode());
}
}
public class MyClass
{
public string Type { get; set; }
public int Id { get; set; }
public override int GetHashCode()
{
return (Type.GetHashCode() % 0x8000) | (int)((uint)Id.GetHashCode() & 0xFFFF0000);
}
}
public class MyClassList : IList<MyClass>
{
List<MyClass> internalList;
int hashCode = 0;
public MyClassList()
{
internalList = new List<MyClass>();
}
private void IncludeInHash(MyClass item)
{
hashCode ^= item.GetHashCode();
}
private void ExcludeFromHash(MyClass item)
{
IncludeInHash(item);
}
public override int GetHashCode()
{
return hashCode;
}
public int IndexOf(MyClass item)
{
return internalList.IndexOf(item);
}
public void Insert(int index, MyClass item)
{
internalList.Insert(index, item);
// Make sure Insert is successful (doesn't throw an exception) before affecting the hash
IncludeInHash(item);
}
public void RemoveAt(int index)
{
MyClass reduce = internalList[index];
internalList.RemoveAt(index);
// Make sure RemoveAt is successful before affecting the hash
ExcludeFromHash(reduce);
}
public MyClass this[int index]
{
get
{
return internalList[index];
}
set
{
MyClass reduce = internalList[index];
internalList[index] = value;
// Make sure these happen atomically; don't allow exceptions to prevent these from being accurate.
ExcludeFromHash(reduce);
IncludeInHash(value);
}
}
public void Add(MyClass item)
{
internalList.Add(item);
IncludeInHash(item);
}
public void Clear()
{
internalList.Clear();
hashCode = 0;
}
public bool Contains(MyClass item)
{
return internalList.Contains(item);
}
public void CopyTo(MyClass[] array, int arrayIndex)
{
internalList.CopyTo(array, arrayIndex);
}
public int Count
{
get { return internalList.Count; }
}
public bool IsReadOnly
{
get { return false; }
}
public bool Remove(MyClass item)
{
if (internalList.Remove(item))
{
ExcludeFromHash(item);
return true;
}
else
return false;
}
public IEnumerator<MyClass> GetEnumerator()
{
return internalList.AsReadOnly().GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}