发布时间:2023-03-11 10:30
关键词:C# List 集合 交集、并集、差集、去重, 对象集合、 对象、引用类型、交并差、List
有时候看官网文档是最高效的学习方式!
一、简单集合
Intersect 交集,Except 差集,Union 并集
int[] oldArray = { 1, 2, 3, 4, 5 };
int[] newArray = { 2, 4, 5, 7, 8, 9 };
var jiaoJi = oldArray.Intersect(newArray).ToList();//2,4,5
var oldChaJi = oldArray.Except(newArray).ToList();//1,3
var newChaJi = newArray.Except(oldArray).ToList();//7,8,9
var bingJi = oldArray.Union(newArray).ToList();//1,2,3,4,5,7,8,9
二、对象集合
Product[] store1 ={new Product { Name = "apple", Code = 9},new Product { Name = "orange", Code = 4}
};
Product[] store2={new Product { Name = "apple", Code = 9},new Product { Name = "lemon", Code = 12}
};
IEnumerable union =store1.Union(store2,newProductComparer());
IEnumerable except=store1.Except(store2,newProductComparer());
IEnumerable intersect=store1.Intersect(store2,newProductComparer());
IEnumerable distinct=store1.Distinct(store2,new ProductComparer());
小提示:
1:IEnumerable 可以简化为 匿名类型 var
对自己去重:
var distinct=store1.Distinct(new ProductComparer());
相对于别人去重
var distinct=store1.Distinct(store2,new ProductComparer());
2: 可以继续进行一些linq或拉姆达操作var distinct=store1.Distinct(store2,new ProductComparer()).OrderBy(c=>c.Code);
原因是引用了linq组件:using System.Linq;
三、比较类的实现
public class Product
{
public string Id {get;set}
public string Name { get; set; }
public int Code { get; set; }
}
1只有一个比较条件
//如果对象存在唯一主键,例如:从数据库里查询出来的数据存在 ID
class ProductComparer : IEqualityComparer{//Products are equal if their names and product numbers are equal.
public boolEquals(Product x, Product y)
{//Check whether the compared objects reference the same data.
if (Object.ReferenceEquals(x, y)) return true;//Check whether any of the compared objects is null.
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))return false;//Check whether the products' properties are equal.
return x.ID ==y.ID;
}//If Equals() returns true for a pair of objects//then GetHashCode() must return the same value for these objects.
public intGetHashCode(Product product)
{//Check whether the object is null
if (Object.ReferenceEquals(product, null)) return 0;//Get hash code for the Code field.
int hashID =product.ID.GetHashCode();//Calculate the hash code for the product.
returnhashID;
}
}
2 多个比较条件
//如果存在组合主键或组合唯一索引,即多个字段组合才能确定唯一性。//Custom comparer for the Product class
class ProductComparer : IEqualityComparer{//Products are equal if their names and product numbers are equal.
public boolEquals(Product x, Product y)
{//Check whether the compared objects reference the same data.
if (Object.ReferenceEquals(x, y)) return true;//Check whether any of the compared objects is null.
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))return false;//Check whether the products' properties are equal.
return x.Code == y.Code && x.Name ==y.Name;
}//If Equals() returns true for a pair of objects//then GetHashCode() must return the same value for these objects.
public intGetHashCode(Product product)
{//Check whether the object is null
if (Object.ReferenceEquals(product, null)) return 0;//Get hash code for the Name field if it is not null.
int hashProductName = product.Name == null ? 0: product.Name.GetHashCode();//Get hash code for the Code field.
int hashProductCode =product.Code.GetHashCode();//Calculate the hash code for the product.
return hashProductName ^hashProductCode;
}
}
3 难道我们每次都要“简单重复的”继承IEqualityComparer接口,来重新实现一个“几乎完全相同的”的Compare类吗?
对于只有一个比较条件的简单情况,我们可以直接对 Distinct、Union、Except、Intersect 进行封装,简单通用方法:
来源:C#list去重, https://www.cnblogs.com/hao-1234-1234/p/8855218.html
public class Compare : IEqualityComparer{
private Func_getField;
public Compare(Funcgetfield)
{
this._getField =getfield;
}
public boolEquals(T x, T y)
{
return EqualityComparer.Default.Equals(_getField(x), _getField(y));
}
public intGetHashCode(T obj)
{
return EqualityComparer.Default.GetHashCode(this._getField(obj));
}
}
public static classCommonHelper
{
///
/// 自定义Distinct扩展方法
///
/// 要去重的对象类
/// 自定义去重的字段类型
/// 要去重的对象
/// 获取自定义去重字段的委托
///
public static IEnumerable MyDistinct(this IEnumerable source, Funcgetfield)
{
return source.Distinct(new Compare(getfield));
}
}
然后这么使用:store1.MyDistinct(s=>s.Id).ToList();
Id 是用于较的属性(或字段),它是可以是任何一个属性。
4、多个比较条件 的通用方法如何实现?
类似于 store1.MyDistinct(s=>s.Id&&Name).ToList();
四、微软官方文档
union :https://docs.microsoft.com/zh-cn/dotnet/api/system.linq.enumerable.union?view=netframework-4.8
intersect:https://docs.microsoft.com/zh-cn/dotnet/api/system.linq.enumerable.intersect?view=netframework-4.8
except:https://docs.microsoft.com/zh-cn/dotnet/api/system.linq.enumerable.except?view=netframework-4.8
distinct:https://docs.microsoft.com/zh-cn/dotnet/api/system.linq.enumerable.distinct?view=netframework-4.8
合交并差 核心代码是相同的: IEqualityComparer 。
建议在看看文档其它部分,以备后用,文档写的很棒!
例如:join 某些情况与union等效。
五、交集、并集、差集、补集、对称差集 示意图,
后两者后可以有前三者演变而来。补集可以求差或去重、对称差集可以先求差、在求并;
参考过的文章
https://www.oschina.net/code/snippet_222150_16997
http://www.cnblogs.com/flywing/p/5912242.html
https://blog.csdn.net/wizblack/article/details/78796557