KIDDK

Linq To Object 函数介绍

static void Main(string[] args)
{
#region Aggregate 把集合中的元素按照表达式依次执行
{
IEnumerable<int> list = new List<int>
{
1,2,3,11
};
int z1 = list.Aggregate((x, y) => x + y); // (((1+2)+3)+4)
Console.WriteLine(z1.ToString());
int z2 = list.Aggregate(3, (x, y) => x + y); //((((3+1)+2)+3)+4)
Console.WriteLine(z2.ToString());
int z3 = list.Aggregate(0, (x, y) => x + y, x => x * 2); // (((1+2)+3)+4) * 2
Console.WriteLine(z3.ToString());
Console.WriteLine("*****************************Aggregate*******************************");
}
#endregion
#region All 判断集合中的每个元素是否都匹配某个表达式
{
IEnumerable<int> list = new List<int>
{
1,2,3,11
};
bool pd1 = list.All(x => x > 10);
bool pd2 = list.All(x => x < 10);
Console.WriteLine(pd1.ToString());
Console.WriteLine(pd2.ToString());
Console.WriteLine("*****************************All*******************************");
}
#endregion
#region Any 判断集合是否为空或者判断结合中某个元素满足表达式的条件
{
List<int> list = new List<int>();
bool angPd = list.Any(); //集合中没有元素false
Console.WriteLine(angPd);
list.Add(1);
angPd = list.Any(); //集合中有元素true
Console.WriteLine(angPd);
IEnumerable<int> list1 = new List<int>
{
1,2,3,11
};
angPd = list1.Any(x => x > 10);//集合中只要有一个元素满足表达式条件就为true 否则为false
Console.WriteLine(angPd);
angPd = list1.Any(x => x > 12);
Console.WriteLine(angPd);
angPd = list1.Any(x => x < 11);
Console.WriteLine(angPd);
Console.WriteLine("*****************************Any*******************************");
}
#endregion
#region AsEnumerable 转换一个远程IQueryable类型为本地IEnumerable 类型
{
DataTable table = new DataTable();
EnumerableRowCollection rows = table.AsEnumerable();
Console.WriteLine("*****************************AsEnumerable*******************************");
}
#endregion
#region Average 如果类型为Nullable<T>类型则在算集合平均数的时候抛弃掉所有null的值然后计算平均值能够有的类型为int,long,double,float,decimal和他们的Nullable版本
//int
{
List<int> intList = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
double intAven = intList.Average();
Console.WriteLine(intAven);
List<int?> intNulList = new List<int?> { 1, 2, 3, null, null, null, 7, 8, 9, 10 };
double? intNullAven = intNulList.Average();
Console.WriteLine(intNullAven);
Console.WriteLine("*****************************Average*******************************");
}
#endregion
#region Cast 转换一个继承IEnumerable的非泛型版本为IEnumerable<T> 如果无法转换则抛出异常
{
string[] sList = new string[3] { "1", "2", "3" };
IEnumerable<string> intCaseList = sList.Cast<string>();
foreach (var item in intCaseList)
{
Console.WriteLine(item.ToString());
}
Console.WriteLine("*****************************Cast*******************************");
}
#endregion
#region Concat 将List<T1> 和 List<T2> 合并为 List<T> 不去除重复项
{
List<int> concatList1 = new List<int> { 1, 2, 3, 4, 5};
List<int> concatList2 = new List<int> { 5, 6, 7, 8 };
IEnumerable<int> concatList3 = concatList1.Concat(concatList2);
foreach (var item in concatList3)
{
Console.WriteLine(item.ToString());
}
Console.WriteLine("*****************************Concat*******************************");
}
#endregion
#region Contains 比较一个T 是否存在于List<T> 可以继承IEqualityComparer<T>接口来指定判断依据
{
IEnumerable<int> a = new List<int> { 1, 2, 3, 4, 5, 6 };
bool containsPd = a.Contains(1);
Console.WriteLine(containsPd);
List<People> peoples = new List<People> {
new People
{
Name = "王"
}};
People people2 = new People
{
Name = "王"
};
containsPd = peoples.Contains(people2, new People());
Console.WriteLine(containsPd);
Console.WriteLine("*****************************Contains*******************************");
}
#endregion
#region Count 获得集合中的元素数量，或者得到满足一个表达式的所有元素的数量
{
IEnumerable<int> countList = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int count1 = countList.Count();
int count2 = countList.Count(x => x > 5);
Console.WriteLine(count1);
Console.WriteLine(count2);
Console.WriteLine("*****************************Count*******************************");
}
#endregion
#region DefaultIfEmpty 如果集合中有元素则返回集合值如果为空则返回集合类型的默认值，并且如果DefaultIfEmpty设置了空集合的默认值，则会返回一个包含了默认值的集合
{
IEnumerable<int> defaultIfEmptyList = new List<int> { };
foreach (var item in defaultIfEmptyList.DefaultIfEmpty())
{
Console.WriteLine(item);
};//值类型返回0
IEnumerable<People> peList = new List<People> { };
foreach (var item in peList.DefaultIfEmpty())
{
if (item == null)
Console.WriteLine("null");
else
Console.WriteLine(item.GetType());
};//引用类型返回null
IEnumerable<bool> bList1 = new List<bool> { };
foreach (var item in bList1.DefaultIfEmpty())
{
Console.WriteLine(item);
};//布尔类型返回false
List<int> list3 = new List<int> { };
list3 = defaultIfEmptyList.DefaultIfEmpty(5).ToList();
Console.WriteLine(list3[0]);
Console.WriteLine("*****************************DefaultIfEmpty*******************************");
}
#endregion
#region Distinct Distinct将去除重复的集合中的数据并返回一个新集合，如果集合类型是引用类型需要一个继承IEqualityComparer<T>的接口的判断类作为判断条件
{
List<int> list = new List<int> { 1, 2, 3, 4, 5, 5, 6, 6, 7, 8, 8 };
foreach(var item in list.Distinct())
{
Console.WriteLine(item);
}
List<People> peoples = new List<People>
{
new People(){ Name = "王"},
new People(){ Name = "王"}
};
foreach (var item in peoples.Distinct())
{
Console.WriteLine(item.Name);
}
Console.WriteLine("************************************************************");
foreach (var item in peoples.Distinct(new People()))
{
Console.WriteLine(item.Name);
}
Console.WriteLine("*****************************Distinct*******************************");
}
#endregion
#region ElementAt 获得集合中的第n个元素从0开始如果超过集合长度则报错
{
List<int> list = new List<int> { 1, 2, 3, 4, 5, 6, 7 };
var item = list.ElementAt(4);
Console.WriteLine(item);
Console.WriteLine("*****************************ElementAt*******************************");
}
#endregion
#region ElementAtOrDefault 获得集合中的第n个元素从0开始如果超过集合长度则给集合类型默认值
{
List<int> list = new List<int> { 1, 2, 3, 4, 5 };
var item1 = list.ElementAtOrDefault(1);
var item2 = list.ElementAtOrDefault(10);
Console.WriteLine(item1);
Console.WriteLine(item2);
List<People> peoples = new List<People>
{
new People(){ Name = "aa"}
};
var item3 = peoples.ElementAtOrDefault(0);
var item4 = peoples.ElementAtOrDefault(1);
Console.WriteLine(item3);
if (item4 == null)
Console.WriteLine("null");
Console.WriteLine("*****************************ElementAt*******************************");
}
#endregion
#region Empty 获得一个没有分配内存的空的集合
{
IEnumerable<int> list = Enumerable.Empty<int>();
Console.WriteLine("*****************************Empty*******************************");
}
#endregion
#region Except 获得list2中没有的list1元素可以使用继承了IEqualityComparer的类重新定义相等判断
{
IEnumerable<int> list1 = new List<int> { 1, 2, 3, 4, 5, 6 };
IEnumerable<int> list2 = new List<int> { 4, 5, 6, 7, 8, 9 };
IEnumerable<int> list3 = list1.Except(list2);
foreach(var item in list3)
{
Console.WriteLine(item);
}
IEnumerable<People> peoples1 = new List<People>
{
new People{ Name = "王"}
};
IEnumerable<People> peoples2 = new List<People>
{
new People{ Name = "王"}
};
IEnumerable<People> peoples3 = peoples1.Except(peoples2);
foreach(People item in peoples3)
{
Console.WriteLine(item);
}
IEnumerable<People> peoples4 = peoples1.Except(peoples2,new People());
Console.WriteLine(peoples4.Count());
Console.WriteLine("*****************************Except*******************************");
}
#endregion
#region First 获得集合中第一个元素或者返回满足表达式的第一个元素(可以多个元素符合) 如果没有元素则报错
{
IEnumerable<int> list1 = new List<int> { 1, 2, 3, 4, 5 };
int a = list1.First();
Console.WriteLine(a.ToString());
int b = list1.First(x => x > 4);
Console.WriteLine(b.ToString());
Console.WriteLine("*****************************First*******************************");
}
#endregion
#region FirstOrDefault 获得集合中第一个元素或者返回满足表达式的第一个元素如果集合中没有元素则返回集合类型的默认值
{
List<int> list1 = new List<int> { 1, 2, 3, 4, 5 };
int a = list1.FirstOrDefault();
Console.WriteLine(a);
int b = list1.FirstOrDefault(x => x > 4);
Console.WriteLine(b);
int c = list1.FirstOrDefault(x => x > 5);
Console.WriteLine(c);
List<People> peoples = new List<People>();
People people = peoples.FirstOrDefault();
if (people == null)
Console.WriteLine("null");
else
Console.WriteLine(people.Name);
Console.WriteLine("*****************************FirstOrDefault*******************************");
}
#endregion
#region GroupBy 按照给定的key分组
{
IEnumerable<GroupClass> groups1 = new List<GroupClass>
{
new GroupClass(){ Number = 1,Name = "王",Address = "上海"},
new GroupClass(){ Number = 2,Name = "王",Address = "北京"},
new GroupClass(){ Number = 3,Name = "吴",Address = "上海"},
new GroupClass(){ Number = 4,Name = "成",Address = "杭州"},
new GroupClass(){ Number = 5,Name = "成",Address = "杭州"},
new GroupClass(){ Number = 6,Name = "吴",Address = "上海"}

};
var peoples1 = groups1.GroupBy(x => x.Name).Select(item=> new { Name = item.Key,num = item.Sum(x=>x.Number)});//public static IEnumerable<IGrouping<TKey, TSource>> GroupBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector);
foreach(var people in peoples1)
{
Console.WriteLine(people.Name);
Console.WriteLine(people.num);
}
var peoples2 = groups1.GroupBy(x => x.Name, (k, g) => new { name = k, value = g }).Select(item =>new { Name = item.name,num = item.value.Sum(x=>x.Number)} );
foreach(var item in peoples2)
{
Console.WriteLine(item.Name);
Console.WriteLine(item.num);
};
var peoples3 = groups1.GroupBy(x => x.Name, (x) => new {Name = x.Name + "AAA",num = x.Number * 5}, (k, g) => new { name = k, value = g }).Select(item=>new { Name =item.name,value=item.value.Sum(x=>x.num)});
foreach (var item in peoples3)
{
Console.WriteLine(item.Name);
Console.WriteLine(item.value);
};
var peoples4 = groups1.GroupBy(x => x.Name, (x) => new { Name = x.Name + "AAA", num = x.Number * 5, Ve = "3" });
IEnumerable<People> peoples = new List<People>
{
new People{ Name = "a",num = 3,Address = "a1"},
new People{ Name = "a",num = 3,Address = "a2"},
new People{ Name = "b",num = 5,Address = "a3"},
new People{ Name = "b",num = 5,Address = "a4"},
new People{ Name = "b",num = 7,Address = "a5"},
new People{ Name = "c",num = 7,Address = "a6"},
new People{ Name = "d",num = 9,Address = "a7"},
};
var peoples5 = peoples.GroupBy(x => new { x.Name, x.num },x=>x.Address);
foreach (var item in peoples5)
{
Console.WriteLine(item.Key.Name);
Console.WriteLine(item.Key.num);
foreach (var value in item)
{
Console.WriteLine(value);
}
}
Console.WriteLine("*****************************GroupBy*******************************");
}
#endregion
#region GroupJoin 获得一个左连接类似字典的集合
{
List<GClass1> c1 = new List<GClass1>
{
new GClass1{ G1Id = 1,Name = "1"},
new GClass1{ G1Id = 2,Name = "2"},
new GClass1{ G1Id = 3,Name = "3"},
new GClass1{ G1Id = 4,Name = "4"},
new GClass1{ G1Id = 5,Name = "5"},
new GClass1{ G1Id = 6,Name = "6"},
new GClass1{ G1Id = 7,Name = "7"}
};
List<GClass2> c2 = new List<GClass2>
{
new GClass2{ Id = 1,Value = "1a"},
new GClass2{ Id = 1,Value = "1b"},
new GClass2{ Id = 2,Value = "2a"},
new GClass2{ Id = 2,Value = "2b"},
new GClass2{ Id = 2,Value = "2c"},
new GClass2{ Id = 3,Value = "3a"},
new GClass2{ Id = 3,Value = "3b"},
new GClass2{ Id = 4,Value = "4a"},
new GClass2{ Id = 9,Value = "9a"}
};
var list = c1.GroupJoin(c2, x => x.G1Id, y => y.Id, (x, y) => new { x, y });
Console.WriteLine("*****************************GroupJoin*******************************");
}
#endregion
#region Intersect 返回 list1和list2中相同的数据或者根据表达式规则返回
{
IEnumerable<int> list1 = new List<int> { 1, 2, 3, 4, 5 };
IEnumerable<int> list2 = new List<int> { 2, 3, 4, 5, 6 };
IEnumerable<int> list3 = list1.Intersect(list2);
foreach (var item in list3)
{
Console.WriteLine(item);
}
IEnumerable<People> peoples1 = new List<People>
{
new People { Name = "王"}
};
IEnumerable<People> peoples2 = new List<People>
{
new People { Name = "王"}
};
IEnumerable<People> list4 = peoples1.Intersect(peoples2);
IEnumerable<People> list5 = peoples1.Intersect(peoples2,new People());
Console.WriteLine(list4.Count());
Console.WriteLine(list5.Count());
Console.WriteLine("*****************************Intersect*******************************");
}
#endregion
#region Join 连接2个集合
{
List<GClass1> c1 = new List<GClass1>
{
new GClass1{ G1Id = 1,Name = "1"},
new GClass1{ G1Id = 2,Name = "2"},
new GClass1{ G1Id = 3,Name = "3"},
new GClass1{ G1Id = 4,Name = "4"},
new GClass1{ G1Id = 5,Name = "5"},
new GClass1{ G1Id = 6,Name = "6"},
new GClass1{ G1Id = 7,Name = "7"}
};
List<GClass2> c2 = new List<GClass2>
{
new GClass2{ Id = 1,Value = "1a"},
new GClass2{ Id = 1,Value = "1b"},
new GClass2{ Id = 2,Value = "2a"},
new GClass2{ Id = 2,Value = "2b"},
new GClass2{ Id = 2,Value = "2c"},
new GClass2{ Id = 3,Value = "3a"},
new GClass2{ Id = 3,Value = "3b"},
new GClass2{ Id = 4,Value = "4a"},
new GClass2{ Id = 9,Value = "9a"}
};

var qure = from a in c1
join b in c2 on a.G1Id equals b.Id
into c3
from c in c3.DefaultIfEmpty()
select
new
{
Id = a.G1Id,
Value = c
};

posted @ 2018-06-22 18:01 KIDDK 阅读(96) 评论(0) 编辑收藏举报

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Linq To Object 函数介绍

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