關鍵詞：C#? List 集合 交集、并集、差集、去重，?對象集合、 對象、引用類型、交并差、List<T>

有時候看官網文檔是最高效的學習方式！

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一、簡單集合

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、對象集合

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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<Product> union =store1.Union(store2,new ProductComparer()); IEnumerable<Product> except=store1.Except(store2,new ProductComparer()); IEnumerable<Product> intersect=store1.Intersect(store2,new ProductComparer()); IEnumerable<Product> distinct=store1.Distinct(store2,new ProductComparer());

小提示：

1：IEnumerable<Product> 可以簡化為 匿名類型 var var distinct=store1.Distinct(store2,new ProductComparer());
2： 可以繼續進行一些linq或拉姆達操作
?var distinct=store1.Distinct(store2,new ProductComparer()).OrderBy（c=>c.Code）; 原因是引用了linq組件：using System.Linq; public class Product {public string Name { get; set; }public int Code { get; set; } }

　核心代碼：簡單情況

//如果對象存在唯一主鍵，例如：從數據庫里查詢出來的數據存在 IDclass ProductComparer : IEqualityComparer<Product> {// Products are equal if their names and product numbers are equal.public bool Equals(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 int GetHashCode(Product product){//Check whether the object is nullif (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.return hashID;}}

核心代碼：復雜情況

// 如果存在組合主鍵或組合唯一索引，即多個字段組合才能確定唯一性。 // Custom comparer for the Product class class ProductComparer : IEqualityComparer<Product> {// Products are equal if their names and product numbers are equal.public bool Equals(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 int GetHashCode(Product product){//Check whether the object is nullif (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;}}

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合交并差 核心代碼是相同的：?IEqualityComparer?。

?三、微軟官方文檔

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 核心代碼是相同的：?IEqualityComparer?。

建議在看看文檔其它部分，以備后用，文檔寫的很棒！

?例如：join 某些情況與union等效。

四、交集、并集、差集、補集、對稱差集 示意圖，

?后兩者后可以有前三者演變而來。補集可以求差或去重、對稱差集可以先求差、在求并；

參考過的文章

https://www.oschina.net/code/snippet_222150_16997

http://www.cnblogs.com/flywing/p/5912242.html

https://blog.csdn.net/wizblack/article/details/78796557

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轉載于:https://www.cnblogs.com/hao-1234-1234/p/10408602.html

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