虽然List里的linq方法（其实是Enumarable的）大部分比较简单 ，但是如果能够灵活运用也是提高code质量，可读性和coding能力的有效途径。而且其中有些方法,例如 Join, 光看注释可能会有点懵。 最近把他们go through了一遍。代码如下。
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Linq; using System.Collections.ObjectModel; using System.Collections; namespace ListMethodTest { public class TestItem { public int number { get; set; } public string str { get; set; } //used for SelectMany public List children { get; set; } public override int GetHashCode() { return number; } } public class InnerClass { public int id { get; set; } public string name { get; set; } } public class ChildTestItem : TestItem { } public class ConvertTest { public int a { get; set; } } public partial class _Default : System.Web.UI.Page { List lst1 = new List (); protected void Page_Load(object sender, EventArgs e) { lst1.Add(new TestItem() { number = 3, str = "dsdfsf", children = new List () { "c1", "c2" } }); lst1.Add(new TestItem() { number = 1, str = "csdfsdf", children = new List () { "c3", "c4" } }); lst1.Add(new TestItem() { number = 2, str = "aasdfsdf" }); lst1.Add(new TestItem() { number = 2, str = "222" }); int part = 3; switch (part) { case 1: Part1();break; case 2: Part2(); break; case 3: Part3(); break; default: break; } } private void Part3() { int sum = lst1.Sum(x => x.number); List take = lst1.Take(3).ToList(); //同样 take前面的 List takewhile = lst1.TakeWhile(x => x.number == 3).ToList(); //key必须唯一 // Dictionary toDic= lst1.ToDictionary(x => x.number); //Ilookup:IEnumerable this[TKey key] { get; } 所以可以有重key ILookup lookup = lst1.ToLookup(x => x.number); //lst1.TrimExcess(); bool trueforall = lst1.TrueForAll(x => x.number > -1); List where = lst1.Where(x => x.number == 2).ToList(); } void Part2() { // 里面的 item和原来的是一个引用，即便 不重写GetHashCode List getR = lst1.GetRange(1, 2); IEnumerable > gb = lst1.GroupBy(x => x.number); int io = lst1.IndexOf(lst1[1]); lst1.Insert(0, new TestItem() { number = 0, str = "00" }); List toInsert = new List () { new TestItem() { number = 0, str = "InsertRange0"}, new TestItem() { number = 2, str = "InsertRange1" }, new TestItem() { number = 9, str = "InsertRange2" }, }; //lst1.InsertRange(0, toInsert); //返回 lst1中与 toInsert 相等的 元素 List Intersect = lst1.Intersect(toInsert, new DistinctTest()).ToList(); List inner = new List () { new InnerClass(){ id=1, name="name1"}, new InnerClass(){ id=2, name="name2"}, new InnerClass(){ id=3, name="name3"}, }; // 2个list的 TKEY 类型必须一致， 返回 key相等的组合 ，其实就是 key相等的 inner join // 最后一个委托只是根据组合 生成 返回的结果 IEnumerable join = lst1.Join(inner, x => x.number, i => i.id, (a, b) => new { a.number, a.str, b.id, b.name }); // 类似 dictionary, lst1为key, 匹配的 InnerClass 的集合为value ，即使集合count为0(没有匹配) ,也会组合 IEnumerable gj = lst1.GroupJoin(inner, x => x.number, i => i.id, (a, b) => new { id = a.number, name = a.str, lst = b }); IEnumerable zip = lst1.Zip(inner, (x, y) => new { x.number, x.str, y.id, y.name }); TestItem last = lst1.Last(x => x.number == 2); int lindex = lst1.LastIndexOf(lst1[2]); int max = lst1.Max(x => x.number); int min = lst1.Min(x => x.number); //lst1.Add(new ChildTestItem()); //IEnumerable ot= lst1.OfType (); List ob = lst1.OrderBy(x => x.str).ToList(); //lst1.Sort((a, b) => { // if( a.number< b.number) return -1; // else if( a.number == b.number) return 0; // else return 1; // } ); // TestItem temp =lst1[0]; // bool remove = lst1.Remove(temp); // int ra= lst1.RemoveAll(x => x.number == 2); // lst1.RemoveAt(2); //lst1.RemoveRange(2, 2); //lst1.Reverse(); // select 是变形用的 ，这个词太唬人了，别被他的外表所蒙蔽 IEnumerable select = lst1.Select(x => new { id = x.number, name = x.str, g = Guid.NewGuid() }); IEnumerable select1 = lst1.Select((x, y) => new { id = x.number, name = x.str, index = y, g = Guid.NewGuid() }); //flatten IEnumerable SelectMany = lst1.SelectMany(x => x.children == null ? new List () : x.children); List s1 = new List () { new TestItem(){ number=1 ,str="sdf" } }; List s2 = new List () { new TestItem(){ number=1 } }; //个数不一样肯定 false bool se = s1.SequenceEqual(s2, new DistinctTest()); List union = s1.Union(s2).ToList(); //不single的话 throw exception //TestItem singe = lst1.Single(x => x.number ==2); List skip = lst1.Skip(2).ToList(); //注意 bypass 前面的element List SkipWhile = lst1.SkipWhile(x => x.number == 0).ToList(); } void Part1() { // ( (item 1,2 的结果 ) 和item 3的结果)和item 4的结果 TestItem agg = lst1.Aggregate((i, j) => { i.number += j.number; return i; }); bool all = lst1.All(i => i.str.Contains("c")); bool any = lst1.Any(i => i.str.Contains("c")); ParallelQuery p = lst1.AsParallel(); IQueryable q = lst1.AsQueryable(); var query = from ti in q where ti.number == 2 select ti; ReadOnlyCollection readonlylst = lst1.AsReadOnly(); double average = lst1.Average(i => i.number); int index = lst1.BinarySearch(new TestItem() { number = 1, str = "123123" }, new CompareClass()); //如果lst1是非泛型的集合 ，转换之后就可以用泛型的方法啦！ where, any ,select , all等 IEnumerable castedLst = lst1.Cast (); List lsttoConcat = new List () { new TestItem() { number = 4 } }; List concatedLst = lst1.Concat(lsttoConcat).ToList(); TestItem t = new TestItem() { number = 4 }; lst1.Add(t); //bool contains = lst1.Contains (t); bool contains = lst1.Contains (new TestItem() { number = 4 }); //bool contains = lst1.Contains ("sdfsdf"); it's wrong! List convertedLst = lst1.ConvertAll(i => new ConvertTest() { a = i.number }); TestItem[] arr = new TestItem[10]; lst1.CopyTo(arr, 3); //下面defLst count 为 0 IEnumerable defLst = lst1.DefaultIfEmpty(); IEnumerable dsicLst = lst1.Distinct(); lst1.Add(new TestItem() { number = 4, str = "sdfsd" }); IEnumerable dsicLst1 = lst1.Distinct (new DistinctTest()); TestItem elementat = lst1.ElementAt(1); TestItem elementatORDefault = lst1.ElementAtOrDefault(10); List toexcept = new List () { lst1[2], lst1[3] }; IEnumerable exceptedLst = lst1.Except(toexcept); bool exist = lst1.Exists(i => i.number == 4); TestItem find = lst1.Find(i => i.number == 4); List findall = lst1.FindAll(i => i.number == 4); int fIndex = lst1.FindIndex(i => i.number == 4); TestItem fLast = lst1.FindLast(i => i.number == 4); int lastIndex = lst1.FindLastIndex(i => i.number == 4); TestItem first = lst1.First(x => x.number == 4); lst1.ForEach(x => x.str = x.number == 4 ? "4" : x.str); } } public class DistinctTest : IEqualityComparer { public bool Equals(TestItem x, TestItem y) { if (x.number == y.number) return true; else return false; } public int GetHashCode(TestItem obj) { //HashCode默认情况就是地址的散列码，跟散列算法有关系,所以默认情况不同对象的hashcode是不一样的，所以要重写TestItem的GetHashCode方法。 //用最简单的方法来说，hashcode就是一个签名。当两个对象的hashcode一样时，两个对象就"有可能"一样。如果不一样的话两个对象就"肯定"不一样。 return obj.GetHashCode(); } } public class CompareClass : IComparer { public int Compare(TestItem x, TestItem y) { if (x.number < y.number) return -1; else if (x.number == y.number) return 0; else return 1; } } } 转载自：