分组操作符

LinqStudy.Test/LinqToObject/GroupTest.cs

@@ -0,0 +1,168 @@
+using System.Collections;
+using System.Collections.Generic;
+
+using System.Linq;
+
+using Xunit;
+
+using LinqStudy;
+
+namespace LinqStudy.Test.LinqToObject
+{
+    /// <summary>
+    /// 分组操作符
+    /// </summary>
+    public class GroupTest
+    {
+        /// <summary>
+        /// GroupBy: 根据指定的键选择器函数对序列的元素进行分组;延迟执行。
+        /// 注意：Key即分组依据，可以常用的值类型，也可以是引用类型(可以自定义比较器))
+        /// </summary>
+        [Fact]
+        public void GroupBy_Default_Test()
+        {
+            List<Person> peoples=new List<Person>()
+            {
+                new Person(){Id=1, Name="Andy", Age=10},
+                new Person(){Id=2, Name="Bab", Age=20},
+                new Person(){Id=3, Name="Babs", Age=20},
+                new Person(){Id=4, Name="Cara", Age=30},
+                new Person(){Id=5, Name="Carlton", Age=30},
+                new Person(){Id=6, Name="Cora", Age=30},
+                new Person(){Id=7, Name="Dawn", Age=40},
+                new Person(){Id=8, Name="Debby", Age=40},
+                new Person(){Id=9, Name="Dotty", Age=40},
+                new Person(){Id=10, Name="Dove", Age=40},
+            };
+
+            var group = peoples.GroupBy(p=>p.Age);
+            var groupCount =  group.Count();
+
+            Assert.Equal(4,groupCount);
+        }
+
+        /// <summary>
+        /// 延迟执行
+        /// </summary>
+        [Fact]
+        public void GroupBy_Delay_Test()
+        {
+            List<Person> peoples=new List<Person>()
+            {
+                new Person(){Id=1, Name="Andy", Age=10},
+                new Person(){Id=2, Name="Bab", Age=20},
+                new Person(){Id=3, Name="Babs", Age=20},
+                new Person(){Id=4, Name="Cara", Age=30},
+                new Person(){Id=5, Name="Carlton", Age=30},
+                new Person(){Id=6, Name="Cora", Age=30},
+            };
+
+            var group = peoples.GroupBy(p=>p.Age);
+
+            //改变数据源
+            List<Person> peoples2=new List<Person>()
+            {
+                new Person(){Id=7, Name="Dawn", Age=40},
+                new Person(){Id=8, Name="Debby", Age=40},
+                new Person(){Id=9, Name="Dotty", Age=40},
+                new Person(){Id=10, Name="Dove", Age=40},
+            };
+            peoples.AddRange(peoples2);
+
+            //受数据源变化的影响，说明是延迟执行。
+            var groupCount =  group.Count();
+
+            Assert.Equal(4,groupCount);
+        }
+    
+        /// <summary>
+        ///  重载：keySelector， comparer
+        ///  key：是引用类型，使用自定义比较器
+        /// </summary>
+        [Fact]
+        public void GroupBy_keySelector_comparer_Test()
+        {
+            List<Teacher> peoples=new List<Teacher>()
+            {
+                new Teacher(){Id=1, Name="河南周口人", Hometown=new Hometown(){Province="河南", City="周口"}},
+                new Teacher(){Id=2, Name="俺河南周口哩", Hometown=new Hometown(){Province="河南",City="周口"}},
+                new Teacher(){Id=3, Name="上海宝山人", Hometown=new Hometown(){Province="上海",City="宝山"}},
+                new Teacher(){Id=4, Name="上海松江人", Hometown=new Hometown(){Province="上海",City="松江"}},
+
+            };
+
+            var group = peoples.GroupBy(p=>p.Hometown,new HometownEqualityComparer());
+
+            var groupFirstNames=group.First().Select(q=>q.Name).ToList();
+            var expected=new List<string>(){"河南周口人","俺河南周口哩"};
+
+            Assert.Equal(expected,groupFirstNames);
+        }
+
+        /// <summary>
+        ///  重载：keySelector， elementSelector
+        ///  key：是引用类型，使用自定义比较器
+        /// </summary>
+        [Fact]
+        public void GroupBy_keySelector_elementSelector_Test()
+        {
+            List<Teacher> peoples=new List<Teacher>()
+            {
+                new Teacher(){Id=1, Name="河南周口人", Hometown=new Hometown(){Province="河南", City="周口"}},
+                new Teacher(){Id=1, Name="俺河南周口哩", Hometown=new Hometown(){Province="河南",City="周口"}},
+                new Teacher(){Id=2, Name="上海宝山人", Hometown=new Hometown(){Province="上海",City="宝山"}},
+                new Teacher(){Id=3, Name="上海松江人", Hometown=new Hometown(){Province="上海",City="松江"}},
+
+            };
+
+            var group = peoples.GroupBy(p=>p.Id,t=>t.Name).ToList();
+
+            var groupFirstNames=group[2].FirstOrDefault();
+            var expected="上海松江人";
+
+            Assert.Equal(expected,groupFirstNames);
+        }
+        /// <summary>
+        /// 重载：keySelector elementSelector comparer
+        /// </summary>
+        [Fact]
+        public void GroupBy_keySelector_elementSelector_comparer_Test()
+        {
+            List<Teacher> peoples=new List<Teacher>()
+            {
+                new Teacher(){Id=1, Name="河南周口人", Hometown=new Hometown(){Province="河南", City="周口"}},
+                new Teacher(){Id=2, Name="俺河南周口哩", Hometown=new Hometown(){Province="河南",City="周口"}},
+                new Teacher(){Id=3, Name="上海宝山人", Hometown=new Hometown(){Province="上海",City="宝山"}},
+                new Teacher(){Id=4, Name="上海松江人", Hometown=new Hometown(){Province="上海",City="松江"}},
+
+            };
+
+            var group = peoples.GroupBy(p=>p.Hometown,t=>t.Name,new HometownEqualityComparer()).ToList();
+
+            var groupFirstNames=group[2].FirstOrDefault();
+            var expected="上海松江人";
+
+            Assert.Equal(expected,groupFirstNames);
+        }
+        
+        [Fact]
+        public void GroupBy_keySelector_resultSelector_Test()
+        {
+            List<Teacher> peoples=new List<Teacher>()
+            {
+                new Teacher(){Id=1, Name="河南周口人", Hometown=new Hometown(){Province="河南", City="周口"}},
+                new Teacher(){Id=1, Name="俺河南周口哩", Hometown=new Hometown(){Province="河南",City="周口"}},
+                new Teacher(){Id=3, Name="上海宝山人", Hometown=new Hometown(){Province="上海",City="宝山"}},
+                new Teacher(){Id=4, Name="上海松江人", Hometown=new Hometown(){Province="上海",City="松江"}},
+
+            };
+
+            var group = peoples.GroupBy(p=>p.Id, (key,teacher) => teacher.Select(t=>t.Name)).ToList();
+
+            var groupFirstNames=group[2].FirstOrDefault();
+            var expected="上海松江人";
+
+            Assert.Equal(expected,groupFirstNames);
+        }
+    }
+}

LinqStudy.Test/LinqToObject/标准查询操作符.md

@@ -31,11 +31,13 @@
 ## 相等操作符
 
 ## 量词操作符
+
     Any
 
     All
 
 ## 分区操作符
+
     Take 返回序列中,从0开始的连续指定项数据子序列；延迟执行。
 
     TakeWhile 

LinqStudy/Models/Hometown.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace LinqStudy
+{
+    /// <summary>
+    /// 家乡类
+    /// </summary>
+    public class Hometown
+    {
+        /// <summary>
+        ///  省份
+        /// </summary>
+        /// <value></value>
+        public string Province{get;set;}
+
+        ///<summary>
+        ///  城市
+        /// </summary>
+        public string City{get;set;}
+    }
+}

LinqStudy/Models/HometownCompare.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace LinqStudy
+{
+    /// <summary>
+    /// 家乡 比较器
+    /// </summary>
+    public class HometownCompare : IComparer<Hometown>
+    {
+        int IComparer<Hometown>.Compare(Hometown x, Hometown y)
+        {
+            int compareResult = 0;
+            
+            if (x == null && y == null)
+            {
+                compareResult = 0;
+            }
+
+            else if (x == null)
+            {
+                compareResult = 1;
+            }
+            else if (y == null)
+            {
+                compareResult = -1;
+            }
+            else
+            {
+                if(x.Province == y.Province)
+                {
+                    compareResult = string.Compare(x.City,y.City);
+                }
+                else
+                {
+                    compareResult = string.Compare(x.Province,y.Province);
+                }
+            }
+
+            return compareResult;
+        }
+    }
+}

LinqStudy/Models/HometownEqualityComparer.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+
+namespace LinqStudy
+{
+    /// <summary>
+    ///  家乡类 相等比较器
+    /// </summary>
+    public class HometownEqualityComparer : IEqualityComparer<Hometown>
+    {
+        bool IEqualityComparer<Hometown>.Equals(Hometown x, Hometown y)
+        {
+            if (x==null || y==null)
+            {
+                return false;
+            }
+
+            return x.Province == y.Province && x.City == y.City;
+        }
+
+        int IEqualityComparer<Hometown>.GetHashCode(Hometown obj)
+        {
+            return (obj.Province+obj.City).GetHashCode();
+        }
+    }
+}

LinqStudy/Models/Person.cs

@@ -3,7 +3,7 @@ using System;
 namespace LinqStudy
 {
     /// <summary>
-    /// 人
+    /// 人类
     /// </summary>
     public class Person
     {

LinqStudy/Models/PersonCompare.cs

@@ -4,7 +4,7 @@ using System.Collections.Generic;
 namespace LinqStudy
 {
     /// <summary>
-    /// Person比较器：Id为比较标准
+    /// Person 比较器
     /// </summary>
     public class PersonComparer : IComparer<Person>
     {

LinqStudy/Models/PersonEqualityComparerByName.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+
+namespace LinqStudy
+{
+    public class PersonEqualityComparerByName : IEqualityComparer<Person>
+    {
+        bool IEqualityComparer<Person>.Equals(Person x, Person y)
+        {
+            if (x==null || y==null)
+            {
+                return false;
+            }
+
+            return x.Name == y.Name;
+        }
+
+        int IEqualityComparer<Person>.GetHashCode(Person obj)
+        {
+            return (obj.Name).GetHashCode();
+        }
+    }
+}

LinqStudy/Models/Teacher.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace LinqStudy
+{
+    /// <summary>
+    /// 老师
+    /// </summary>
+    public class Teacher
+    {
+        /// <summary>
+        /// Id
+        /// </summary>
+        public int Id {get;set;}
+
+        /// <summary>
+        /// 姓名
+        /// </summary>
+        public string Name{get;set;}
+
+        /// <summary>
+        /// 家乡
+        /// </summary>
+        public Hometown Hometown{get;set;}
+    }
+}

LinqStudy/Models/TeacherCompare.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using LinqStudy;
+
+namespace LinqStudy
+{
+    /// <summary>
+    /// 家乡 比较器
+    /// </summary>
+    public class TeacherCompare : IComparer<Teacher>
+    {
+        int IComparer<Teacher>.Compare(Teacher x, Teacher y)
+        {
+            int compareResult = 0;
+            
+            if (x == null && y == null)
+            {
+                compareResult = 0;
+            }
+
+            else if (x == null)
+            {
+                compareResult = 1;
+            }
+            else if (y == null)
+            {
+                compareResult = -1;
+            }
+            else
+            {
+                if(x.Id == y.Id)
+                {
+                    if(x.Name==y.Name)
+                    {
+                        IComparer<Hometown> homeCompare=  new HometownCompare();
+                        compareResult= homeCompare.Compare(x.Hometown, y.Hometown);
+                    }
+                    else
+                    {
+                        compareResult = string.Compare(x.Name,y.Name);
+                    }
+                    
+                }
+                else
+                {
+                    if(x.Id>y.Id)
+                    {
+                        compareResult =1;
+                    }
+                    else
+                    {
+                        compareResult = -1;
+                    }
+                }
+            }
+
+            return compareResult;
+        }
+    }
+}