using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace 测试控制台{ class List集合基础操作 { public static void c() { List<stu> lstu = new List<stu>{ new stu{id=1,name="zs",age=5,pc=1}, new stu{id=3,name="zs",age=4,pc=2}, new stu{id=3,name="zs",age=3,pc=3}, new stu{id=2,name="ls",age=1,pc=1}, new stu{id=4,name="ls",age=1,pc=2}, new stu{id=4,name="ls",age=1,pc=2}, new stu{id=4,name="lr",age=1,pc=2} }; List<stu> lstugroup = lstu; string a = "1,3,2,6,9,9"; string b = "1,3,5,7,9"; string c = "1,3,5,7,9,7"; string d = "1,2,3,4,5,6"; List<string> lsa = a.Split(',').ToList();//数组转ToList集合（using System.Linq;） List<string> lsb = b.Split(',').ToList(); List<string> lsc = c.Split(',').ToList(); List<string> lsd = d.Split(',').ToList(); List<string> lsstr = new List<string>() { "qq", "weibo", "zhihu" }; List<int> lsint = new List<int>() { 1, 2, 5 }; // 1 单个集合 bool bbh = lsa.Contains("2");//是否包含 bool bbh2 = lstu.Exists(s => s.age == 1 && s.id == 5); List<string> lsqc = lsa.Distinct().ToList();//一维去重 List<string> lsqc4 = lstu.Select(p => p.name).Distinct().ToList();//选择name属性并去重 lsa.Sort();//排序，无返回值； lstu = lstu.OrderBy(s => s.id).ThenBy(s => s.age).ToList(); ;// 以id，age排序 decimal sum = lsint.Sum();//合计,list 必须为int等类型 // 2 set操作 两个集合：交差并 集合； bool bjj = lsa.Intersect(lsb).Count() > 0;//判断是否有交集 List<string> lsjj = lsa.Intersect(lsb).ToList();//求交集 1,3,9 List<string> lscj = lsa.Except(lsb).ToList();//求相对差集 相对las得2,6 List<string> lsbj2 = lsa.Union(lsc).ToList();//求并集（并保留重复项） 1,2,3,6,9,9,1,3,5,7,9 List<string> lsbj1 = lsa.Union(lsb).ToList();//求并集（并剔除重复项） 1,2,3,5,6,7,9 lstu = lstu.Skip(2).Take(3).ToList(); //从第二项开始取3个项目；System.Linq.Enumerable stu t = lstu.Find(s => s.id > 2); lstu = lstu.Where(s => s.id > 2).ToList(); //3 group by var ab2 = (from p in lstugroup group p by p.name into g select new { name = g.Key }).ToList();//单属性distinct var ab3 = (from p in lstugroup group p by new { p.name, p.age } into g select new { name = g.Key }).ToList();//多属性distinct //4 过滤 List<stu> ab4 = lstugroup.GroupBy(p => p.id).Select(p => new stu { id = p.Key, name = p.FirstOrDefault().name }).ToList();//单属性distinct并默认其他属性 // 5 linq where findAll 的比较_形式 List<stu> ab5 = (from i in lstugroup where i.id > 3 select i).ToList(); List<stu> ab6 = lstugroup.Where(s => s.id > 3).ToList(); List<stu> ab7 = lstugroup.FindAll(s => s.id > 3);//直接返回该对象，不需要toList() // 6 linq where findAll 的比较_性能 》数据比较功能 where≈findAll > linq List<stu> stuceshi = new List<stu>(); for (int i = 0; i < 100000; i++) { stuceshi.Add(new stu { id = i, name = "name" + i, age = i, mm = "zs" }); } //10w次比对数据 //List<stu> ab8 = (from i in stuceshi where i.mm =="zs" select i).ToList();//11.1742ms //List<stu> ab9 = lstugroup.Where(s => s.mm == "zs").ToList();//0.3283ms //List<stu> ab10 = lstugroup.FindAll(s => s.mm == "zs");//0.3225ms // 8千DM_DORM对象筛选 三者性能略同 string name1; System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch(); sw.Start(); for (int i = 0; i < 1000000; i++) { //name1 = stuceshi.Find(s => s.id == 99999) == null ? "" : stuceshi.Find(s => s.id == 99999).name; //stuceshi = stuceshi.Where(s => s.name == "").ToList(); stuceshi = stuceshi.Where(s => s.name.Length == 0).ToList(); } sw.Stop(); string ts2 = sw.Elapsed.TotalMilliseconds.ToString(); // 7 处理find异常.大量数据时，自己处理异常效率是try catch的6倍； string name3 = lstu.Find(s => s.id == 8) == null ? "" : lstu.Find(s => s.id == 8).name; //string name1 = stuceshi.Find(s => s.id == -1) == null ? "" : stuceshi.Find(s => s.id == -1).name; //3.9594 //string name1 = stuceshi.Find(s => s.id == 99999) == null ? "" : stuceshi.Find(s => s.id == 99999).name; //7.0533 #region try catch情况 18403 //for (int i = 0; i > -1000; i--) // 18403.0000 //{ // try //22.5663 // { // name1 = stuceshi.Find(s => s.id == -1).name; // } // catch (Exception) // { // name1 = ""; // } //} #endregion #region 自处理情况 3250 //for (int i = 0; i > -1000; i--) 时间0.3274~8490.0000(全比较是8490) //{ // name1 = stuceshi.Find(s => s.id == 99999) == null ? "" : stuceshi.Find(s => s.id == 99999).name; //} #endregion // 8双问号操作符 // string strParam= Request.Params["param"]?? ""; int? cc = null; int name4 = cc ?? 0; // 9 StartsWith() lstugroup = lstugroup.Where(s => s.name.StartsWith("l")).ToList(); // 筛选name以l开头； //lstugroup =lstugroup.Where(s => s.name.StartsWith("l")). //10 遍历集合 int ii = 0; foreach (stu item in lstugroup) { ii = lstugroup.IndexOf(item); } //11 处理Where,找不到是count=0而不报错。 lstugroup = lstugroup.Where(s => s.name.StartsWith("m")).ToList(); // 筛选name以l开头； }//断点处 } public class stu { public int id { get; set; } public string name { get; set; } public int age { get; set; } public int pc { get; set; } public string mm { get; set; } }}
