public static void c()
{
List <stu> lstu = new List <stu> {
new stu {
id = 3, name = "zs", age = 1, pc = 0
},
new stu {
id = 3, name = "zs", age = 1, pc = 0
},
new stu {
id = 3, name = "zs", age = 2, pc = 0
},
new stu {
id = 2, name = "ls", age = 2, pc = 0
},
new stu {
id = 4, name = "ls", age = 3, pc = 2
},
new stu {
id = 4, name = "ls", age = 3, pc = 0
},
new stu {
id = 4, name = "lr", age = 4, pc = 2
},
new stu {
id = 4, name = "lr", age = 4, pc = 2
},
new stu {
id = 4, name = "lr", age = 5, pc = 2
}
};
int c8 = lstu.GroupBy(p => p.age).Count() - lstu.Where(c => c.pc != 0).GroupBy(s => s.age).Count();
IEnumerable <IGrouping <int, stu> > aaa = lstu.GroupBy(c => c.age);
foreach (IGrouping <int, stu> sa in aaa)
{
// List<stu> stua = sa.;
}
//lstu.Where(s => s.age == s.age && s.pc != 0).Count();
//lstu.Select(s=>s.pc!=0)
// select * from b group by age
List <stu> lstugroup = lstu;
List <stu> lstugroup0101 = lstu;
string a = "1,3,2,6,9,9";
string b = "1,3,5,7,9";
string c1 = "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 = c1.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
//List<string> lsqc5 = lstu.Count(s=>s.age)
//2,排序，求和
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
decimal sum2 = lstu.Sum(s => s.age);
// 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；
//12
var g2 = lstugroup0101.GroupBy(x => new { x.id, x.age });
//lstugroup0101= g2.Where(v => v.Key ==3).ToList();
List <stu> dddd = new List <stu>();
foreach (var item in g2)
{
foreach (var item2 in item)
{
dddd.Add(item2);
}
}
}//断点处