Linq標準查詢操作子
語言集查詢Ganmge hteg.ratedQuw,LINQ,整合了C#程式語言中的查詢語法,可以用相同的語法存取不同的資料來源。 LINQ提 供了不同資料來源的抽象層 ,所 以可以使用相同的語法。
1篩選運算子
篩選運算子定義了傳回元素的條件。
| 篩選運算子 |
說明 |
| where |
使用謂詞，傳回布林值 |
| OfType< TResult> |
根據型別篩選元素 |
#應用範例：
where用法：
var racers = from r in Formulal.Racers
where r.Wins > 15 && r.Country == "Brazil" select r;
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OfType< T>用法：
object[] data = {"one", 2, "three", 4, 5, "six"};
var rtnData = data.OfType<string>(); //返回类型为string的数据元素集合登入後複製
2投射運算元
把
物件轉換為另一個類型的新物件
#用法範例：
select用法
var racers = from r in Formulal.Racers
where r.Wins > 15 && r.Country == "Brazil"
select new
{
Name = string.Format("{0} {1}", r.FirstName, r.LastName),
Country = r.Country,
Wins = r.Wins
}; //输出为含有Name,Country,Wins共计3个属性的对象集合登入後複製
selectMany用法
var ferrariDrivers = Formulal.Racers.
SelectMany(r => r.Cars,
(r, c) => new { Racer = r, Car = c }).
Where(r => r.Car == "Ferrari").
OrderBy(r => r.Racer.LastName).
Select(r => r.Racer.FirstName + " " + r.Racer.LastName);//筛选出驾驶法拉利的选手集合登入後複製
3排序運算子
#改變傳回元素的順序
##排序運算子| 描述 | |
|---|
OrderBy| #升序排序 | |
OrderByDescending| 降序排序 | |
ThenBy| 第一次排序結果類似，用第二次升序排序 | |
ThenByDescending| 第一次排序結果類似，用第二次降序排序 | |
Reverse| 反轉集合中元素的順序 | |
#範例：
var racers = from r in Formulal.Racers
where r.Country == "Brazil"
orderby r.Wins descending
select new
{
Name = string.Format("{0} {1}", r.FirstName, r.LastName),
Country = r.Country,
Wins = r.Wins
};//国家为巴西，按照胜场次数降序排列登入後複製
4連接
運算子
用於合併不直接相關的集合
連接運算子| 描述 | |
|---|
#Join| 可以根據鍵選擇器函數連接連接2個集合 | |
GroupJoin| 連接兩個集合,組合其結果 | |
//Join连接
//获取冠军年份在2003年后的选手
var racer5 = from r in Formulal.Racers
from y in r.Years
where y > 2003
select new
{
Year = y,
Name = string.Format("{0} {1}", r.FirstName, r.LastName)
}; //获取冠军年份在2003年后的团队
var team1 = from r in Formulal.ChampionTeams
from y in r.Years
where y > 2003
select new
{
Year = y,
Name = string.Format("{0}", r.Name)
}; //连接
var racerAndTeams = from r in racer5
join t in team1 on r.Year equals t.Year
select new
{
Yearj= r.Year,
Racerj = r.Name,
Teamj = t.Name
};登入後複製
Yearj| Racerj | #Teamj | |
|---|
Yearj=2004| Racerj=Michael Schumacher | Teamj =Ferrari | |
Yearj=2005| Racerj=Fernando Alonso | #Teamj =Renault | |
Yearj=2006| Racerj=Fernando Alonso | Teamj =Renault | |
#Yearj= 2007| Racerj=Kimi Räikkönen | Teamj =Ferrari | |
Yearj=2008| Racerj=Lewis Hamilton | Teamj =Ferrari | |
Yearj=2014| #Racerj=Lewis Hamilton | Teamj =Mercedes | |
## Yearj=2015| Racerj=Lewis Hamilton | Teamj =Mercedes | |
Yearj=2009| Racerj=Jenson Button | Teamj =Brawn GP | |
Yearj=2010| Racerj=Sebastian Vettel | Teamj =Red Bull Racing | |
#Yearj=2011| Racerj=Sebastian Vettel | Teamj =Red Bull Racing | |
Yearj=2012| # Racerj=Sebastian Vettel | Teamj =Red Bull Racing | |
Yearj=2013| Racerj=Sebastian Vettel | #Teamj =Red Bull Racing | |
5組合運算子
把資料放在群組中
組合運算符| 描述 | |
|---|
GroupBy| 組合有公共鍵的元素 | |
ToLookUp| 透過建立一個一對多的字典，來組合元素。 | |
GroupBy用法範例：
var countries = from r in Formulal.Racers
group r by r.Country into g
orderby g.Count() descending, g.Key
where g.Count() > 2
select new
{
Country = g.Key,
Count = g.Count()
};//获取冠军次数大于2的国家登入後複製
結果：
UK10
#Brazil3
Finland3 | |
#如果分組需要根據多個欄位| ，則應該這樣寫： | //按组合键分组后，每组元素个数大于2的分组，按降序排序
var rtnByVal1 = from item in dataSource
group item by new { item.Val1, item.Val2 }
into g
where g.Count()>1
orderby g.Count() descending
select g; //按Val1和Val2组合为字典键，元素个数为值
var dict = rtnByVal1.ToDictionary(g=>g.First(),g=>g.Count());登入後複製
6 | 量詞
運算子| #如果元素序列滿足指定的條件,量詞運算子就傳回布林值 | | 組合運算子
描述 | |
#Any
###確定集合中是否有滿足謂詞函數的元素###############All##########決定集合中是否都滿足謂詞函數的元素########## ##Contains######檢查某個元素是否存在集合中#############
List<int> intList1 = new List<int>(5) {1, 2, 3, 4, 5};
bool any3 = intList1.Any(r => r == 3);//确定集合中是否有3，返回true
bool any0 = intList1.Any(r => r == 0);//确定集合中是否有0，返回false
bool allMoreZero = intList1.All(r => r > 0);//确定序列中所有元素都满足大于0，返回true
bool allMore2 = intList1.All(r => r > 2); //返回false
bool contains3 = intList1.Contains(3); //元素3是否在集合中，true登入後複製
7分区操作符
分区操作符，返回一个子集。使用它们可以得到部分结果。
| 分区运算符 | 描述 |
|---|
| Take | 必须制定提取元素的个数 |
| Skip | 跳过指定的元素个数，提取其他元素 |
| TakeWhile | 提取条件为真的元素 |
| SkipWhile | 跳过条件为真的元素 |
int pageSize = 5;
int numberPages = (int)Math.Ceiling(Formulal.Racers.Count() / (double)pageSize);
for (int page = 0; page < numberPages; page++)
{ var racersPartition =
(from r in Formulal.Racers
orderby r.LastName, r.FirstName
select r.FirstName + " " + r.LastName).Skip(page * pageSize).Take(pageSize);
}登入後複製
结果：
Page 0Fernando Alons
Mario Andretti
Alberto Ascari
Jack Brabham
Jenson ButtonPage 1Jim Clark
Juan Manuel Fa
Nino Farina
Emerson Fittipaldi
Mika Hakkinen
Page 2Lewis Hamilton
Mike Hawthorn
Damon Hill
Graham Hill
Phil Hill
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8集合操作符（Set operators）
集合操作符返回 一 个集合。除了Distinct之外，其他都需要2个集合。
| 集合操作符 | 描述 |
|---|
| Distinct | 从集合中删除重复的元素 |
| Union | 返回出现在其中一个集合中的唯一元素 |
| Intersect | 交集 |
| Except | 只出现在一个集合中的元素 |
| Zip | 通过使用指定的谓词函数合并2个集合 |
应用举例：
List<int> intList1 = new List<int>(5) {1, 2, 3, 4, 5,3};
List<int> intList2 = new List<int>(3) {2, 5, 0};
var delDuplic = intList1.Distinct(); //去重，结果{1,2,3,4,5}
var unionList = intList1.Union(intList2); //并集,结果{1,2,3,4,5,0}
var interList = intList1.Intersect(intList2); //交集，结果{2,5}
var exceptList = intList1.Except(intList2);//差集，结果{1,3,4}
var exceptList2 = intList2.Except(intList1);//差集，结果{0}
var unionList2 = intList1.Zip(intList2,((i1, i2) => i1+", "+i2)); 结果：{{1,2}{2,5}{3,0}}登入後複製
9元素操作符（Element operators）
这些元素操作符仅返回一 个元素。
| 元素操作符 | 描述 |
|---|
| First | 返回第一个满足条件的元素 |
| FirstOrDefault | 返回第一个满足条件的元素，但如果没有找到满足条件的元素,就返回类型的默认值 |
| Last | 返回最后一个满足条件的元素 |
| LastOrDefault | 返回最后一个满足条件的元素，但如果没有找到满足条件的元素,就返回类型的默认值 |
| ElementAt | 指定了要返回的元素的位置 |
| ElementAtOrDefault | 指定了要返回的元素的位置，但如果没有找到满足条件的元素,就返回类型的默认值 |
| Single | 只返回一个满足条件的元素，如果有多个满足条件，就抛出一个异常。 |
| SingleOrDefault | 只返回一个满足条件的元素，但如果没有找到满足条件的元素,就返回类型的默认值 |
应用举例：
List<int> intList1 = new List<int>(5) { 1, 8, 3, 4, 5, 3 };
int firstMore1 = intList1.First(r => r > 1);//结果：8
int firstMore17 = intList1.FirstOrDefault(r => r > 17); //结果：0（因为不存在）
int lastMore3 = intList1.Last(r => r > 3); //结果5
int last = intList1.ElementAt(2); //结果3,（索引从0开始）登入後複製
10聚合操作符（Aggregate operators）
聚合操作符计算集合的一个值。利用这些聚合操作符 ,可 以计算所有值的总和、所有元
素的个数、值最大和最小的元素 ,以 及平均值等
| 聚合操作符 | 描述 |
|---|
| Count | 所有值的个数 |
| Sum | 所有值的综合 |
| Min | 所有值的的最小值 |
| Max | 所有值的的最大值 |
| Average | 所有值的平均数 |
public class MyIntClass
{
public string Name { get; set; }
public int Integar { get; set; }
public MyIntClass(string name, int i)
{
this.Name = name;
this.Integar = Integar;
}
}
List<MyIntClass> intList1 = new List<MyIntClass>(5)
{
new MyIntClass("first",1),
new MyIntClass("second",8) ,
new MyIntClass("third",3) ,
new MyIntClass("fourth",4) ,
new MyIntClass("fifth",5) ,
new MyIntClass("sixth",3)
};
int count = intList1.Count;
int sum = intList1.Sum(r=>r.Integar);
int min = intList1.Min(r => r.Integar);
int max = intList1.Max(r => r.Integar);
double average = intList1.Average(r => r.Integar);登入後複製
11转换操作符（Conversion operators）
转换操作符将集合转换为数组 :IEnumberable、 IList, IDictionary 等。
| Conversion operators | 描述 |
|---|
| ToArray | 集合转化为Array |
| AsEnumerable | 返回类型为IEnumerable< T> |
| ToList | 集合转化为List |
| ToDictionary | 集合转化为Dictionary |
| Cast< TResult> | 映射 |
还是上面的例子
IEnumerable<MyIntClass> ienuList = from r in intList1 where r.Integar > 3 select r; //返回默认的IEnumerable集合
List<MyIntClass> ienuList2 = (from r in intList1 where r.Integar > 3 select r).ToList(); //返回List
MyIntClass[] ienuList2 = (from r in intList1 where r.Integar > 3 select r).ToArray();//返回数组
var dict = (from r in intList1 where r.Integar > 3 select r).ToDictionary(r=>r.Name,r=>r.Integar);
//字典，key是name, value：Integar
IEnumerable<MyIntClass> ienuList2 = (from r in intList1 where r.Integar > 3 select r).AsEnumerable();登入後複製
12生成操作符（Generation operators）
这些生成操作符返回 一 个新集合
| Generation operators | 描述 |
|---|
| Empty | 集合是空的 |
| Range | 返回一系列数字 |
| Repeat | 返回始终重复一个值的集合 |
IEnumerable<int> ints = Enumerable.Range(3, 10);
//{3,4,5,6,7,8,9,10,11,12}IEnumerable<int> emptyInts = Enumerable.Empty<int>();
//生成一个空集合IEnumerable<int> ints2= Enumerable.Repeat(6,8);//生成8个6的集合登入後複製
附：展示所用到的实体类和数据
选手实体类
//选手实体类
public class Racer
{
public Racer(string firstName = null, string lastName = null,
string country = null, int starts = 0,int wins = 0, IEnumerable<int> years = null, IEnumerable<string> cars = null)
{
this.FirstName = firstName;
this.LastName = lastName;
this.Country = country;
this.Starts = starts;
this.Wins = wins;
var yearList = new List<int>();
if (years != null)
{
foreach (var year in years)
{
yearList.Add(year);
} this.Years = yearList.ToArray();
} if (cars != null)
{ var carList = new List<string>();
foreach (var car in cars)
{
carList.Add(car);
}
this.Cars = carList.ToArray();
} public string FirstName { get; set; }
public string LastName { get; set; } //赢得比赛的次数
public int Wins { get; set; } //所属国家
public string Country { get; set; } //开始做的年龄
public int Starts { get; set; } //车型数组
public string[] Cars { get; private set; } //赢得冠军的年份
public int[] Years { get; private set; }
}
}登入後複製
选手数据
//选手List
public static List<Racer> Racers = new List<Racer>(40)
{
new Racer("Nino", "Farina", "Italy", 33, 5, new int[] { 1950 }, new string[] { "Alfa Romeo" }), new Racer("Alberto", "Ascari", "Italy", 32, 10, new int[] { 1952, 1953 }, new string[] { "Ferrari" }), new Racer("Juan Manuel", "Fangio", "Argentina", 51, 24, new int[] { 1951, 1954, 1955, 1956, 1957 }, new string[] { "Alfa Romeo", "Maserati", "Mercedes", "Ferrari" }), new Racer("Mike", "Hawthorn", "UK", 45, 3, new int[] { 1958 }, new string[] { "Ferrari" }), new Racer("Phil", "Hill", "USA", 48, 3, new int[] { 1961 }, new string[] { "Ferrari" }), new Racer("John", "Surtees", "UK", 111, 6, new int[] { 1964 }, new string[] { "Ferrari" }), new Racer("Jim", "Clark", "UK", 72, 25, new int[] { 1963, 1965 }, new string[] { "Lotus" }), new Racer("Jack", "Brabham", "Australia", 125, 14, new int[] { 1959, 1960, 1966 }, new string[] { "Cooper", "Brabham" }), new Racer("Denny", "Hulme", "New Zealand", 112, 8, new int[] { 1967 }, new string[] { "Brabham" }), new Racer("Graham", "Hill", "UK", 176, 14, new int[] { 1962, 1968 }, new string[] { "BRM", "Lotus" }), new Racer("Jochen", "Rindt", "Austria", 60, 6, new int[] { 1970 }, new string[] { "Lotus" }), new Racer("Jackie", "Stewart", "UK", 99, 27, new int[] { 1969, 1971, 1973 }, new string[] { "Matra", "Tyrrell" }), new Racer("Emerson", "Fittipaldi", "Brazil", 143, 14, new int[] { 1972, 1974 }, new string[] { "Lotus", "McLaren" }), new Racer("James", "Hunt", "UK", 91, 10, new int[] { 1976 }, new string[] { "McLaren" }), new Racer("Mario", "Andretti", "USA", 128, 12, new int[] { 1978 }, new string[] { "Lotus" }), new Racer("Jody", "Scheckter", "South Africa", 112, 10, new int[] { 1979 }, new string[] { "Ferrari" }), new Racer("Alan", "Jones", "Australia", 115, 12, new int[] { 1980 }, new string[] { "Williams" }), new Racer("Keke", "Rosberg", "Finland", 114, 5, new int[] { 1982 }, new string[] { "Williams" }), new Racer("Niki", "Lauda", "Austria", 173, 25, new int[] { 1975, 1977, 1984 }, new string[] { "Ferrari", "McLaren" }), new Racer("Nelson", "Piquet", "Brazil", 204, 23, new int[] { 1981, 1983, 1987 }, new string[] { "Brabham", "Williams" }), new Racer("Ayrton", "Senna", "Brazil", 161, 41, new int[] { 1988, 1990, 1991 }, new string[] { "McLaren" }), new Racer("Nigel", "Mansell", "UK", 187, 31, new int[] { 1992 }, new string[] { "Williams" }), new Racer("Alain", "Prost", "France", 197, 51, new int[] { 1985, 1986, 1989, 1993 }, new string[] { "McLaren", "Williams" }), new Racer("Damon", "Hill", "UK", 114, 22, new int[] { 1996 }, new string[] { "Williams" }), new Racer("Jacques", "Villeneuve", "Canada", 165, 11, new int[] { 1997 }, new string[] { "Williams" }), new Racer("Mika", "Hakkinen", "Finland", 160, 20, new int[] { 1998, 1999 }, new string[] { "McLaren" }), new Racer("Michael", "Schumacher", "Germany", 287, 91, new int[] { 1994, 1995, 2000, 2001, 2002, 2003, 2004 }, new string[] { "Benetton", "Ferrari" }), new Racer("Fernando", "Alonso", "Spain", 252, 32, new int[] { 2005, 2006 }, new string[] { "Renault" }), new Racer("Kimi", "Räikkönen", "Finland", 230, 20, new int[] { 2007 }, new string[] { "Ferrari" }), new Racer("Lewis", "Hamilton", "UK", 166, 43, new int[] { 2008, 2014, 2015 }, new string[] { "McLaren", "Mercedes" }), new Racer("Jenson", "Button", "UK", 283, 15, new int[] { 2009 }, new string[] { "Brawn GP" }), new Racer("Sebastian", "Vettel", "Germany", 156, 42, new int[] { 2010, 2011, 2012, 2013 }, new string[] { "Red Bull Racing" })
};登入後複製
团队实体类
[Serializable] public class Team
{ public Team(string name, params int[] years)
{ this.Name = name;
this.Years = years;
} public string Name { get; private set; }
public int[] Years { get; private set; }
}登入後複製
团队数据
//冠军团队List
public static List<Team> ChampionTeams = new List<Team>()
{ new Team("Vanwall", 1958),
new Team("Cooper", 1959, 1960),
new Team("Ferrari", 1961, 1964, 1975, 1976, 1977, 1979, 1982, 1983, 1999, 2000, 2001, 2002, 2003, 2004, 2007,
2008),
new Team("BRM", 1962),
new Team("Lotus", 1963, 1965, 1968, 1970, 1972, 1973, 1978),
new Team("Brabham", 1966, 1967),
new Team("Matra", 1969),
new Team("Tyrrell", 1971),
new Team("McLaren", 1974, 1984, 1985, 1988, 1989, 1990, 1991, 1998),
new Team("Williams", 1980, 1981, 1986, 1987, 1992, 1993, 1994, 1996, 1997),
new Team("Benetton", 1995),
new Team("Renault", 2005, 2006),
new Team("Brawn GP", 2009),
new Team("Red Bull Racing", 2010, 2011, 2012, 2013),
new Team("Mercedes", 2014, 2015)
};登入後複製
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