提供一组静态方法用于查询实现IEnumerable<T>的对象。
Methods
1.Aggregate
在序列上应用累加器函数。指定的值作为初始累加器值，指定的函数用于选择结果。
List<String> fruits = new List<string>();
fruits.AddRange(new string[] { "apple", "mango", "orange", "passionfruit"});
string longestName = fruits.Aggregate("banana", (longest, next) => next.Length > longest.Length ? next : longest, fruit => fruit.ToUpper());
Console.WriteLine("the fruit with longest name is {0}.", longestName);
//the fruit with longest name is PASSIONFRUIT.2.All
判断序列的所有值是否都满足特定条件。
public class Pet {
public string Name {
get;
set;
}
public int Age {
get;
set;
}
}
public class Person {
public string LastName {
get;
set;
}
public Pet[] Pets {
get;
set;
}
}List<Person> people = new List<Person>{
new Person{LastName = "Haas", Pets =
new Pet[]{
new Pet{Name = "Barley", Age = 10},
new Pet{Name = "Boots", Age = 14},
new Pet{Name = "Whiskers", Age = 6},
}},
new Person{
LastName = "Fakhouri",
Pets =
new Pet[]{
new Pet{Name = "Snowball", Age = 1},
},
},
new Person{LastName = "Antebi", Pets =
new Pet[]{
new Pet{Name = "Belle", Age = 8},
}},
new Person{LastName = "Philips", Pets = new Pet[]{
new Pet{Name = "Sweetie", Age = 2},
new Pet{Name = "Rover", Age = 13},
}}};
//筛选所有宠物年龄大于5的所有人
IEnumerable<string> allownpetgt5names =
from person in people where
person.Pets.All(pet => pet.Age > 5) select person.LastName;
foreach (string name in allownpetgt5names) {
Console.WriteLine(name);
}
// All
Console.WriteLine("all pet`s age >5: {0}",
people[0].Pets.All(i => i.Age > 5)); // True3.Any
List<Person> people = new List<Person>{
new Person{LastName = "Haas", Pets =
new Pet[]{
new Pet{Name = "Barley", Age = 10},
new Pet{Name = "Boots", Age = 14},
new Pet{Name = "Whiskers", Age = 6},
}},
new Person{
LastName = "Fakhouri",
Pets =
new Pet[]{
new Pet{Name = "Snowball", Age = 1},
},
},
new Person{LastName = "Antebi", Pets =
new Pet[]{
new Pet{Name = "Belle", Age = 8},
}},
new Person{LastName = "Philips", Pets = new Pet[]{
new Pet{Name = "Sweetie", Age = 2},
new Pet{Name = "Rover", Age = 13},
}}};
//筛选所有宠物年龄大于5的所有人
IEnumerable<string> allownpetgt5names =
from person in people where
person.Pets.All(pet => pet.Age > 5) select person.LastName;
foreach (string name in allownpetgt5names) {
Console.WriteLine(name);
}
// Any
Console.WriteLine("any pet`s age >5: {0}",
people[3].Pets.Any(i => i.Age > 5)); // True4.Append
List<int> numbers = new List<int>{1, 2, 3, 4};
numbers.Append(5);
Console.WriteLine(string.Join(",", numbers)); // 1,2,3,4
Console.WriteLine(string.Join(",", numbers.Append(5))); // 1,2,3,4,5
List<int> newNumbers = numbers.Append(5).ToList();
Console.WriteLine(string.Join(",", newNumbers)); // 1,2,3,4,55.AsEnumerable
class Clump<T> : List<T> {
public IEnumerable<T> Where(Func<T, bool> predicate) {
Console.WriteLine("In Clump`s implmentation of Where().");
return Enumerable.Where(this, predicate);
}
}Clump<string> fruitClump =
new Clump<string>{"apple", "passionfruit", "banana", "mongo",
"orange", "blueberry", "grape", "strawberry"};
// first: call clump`s Where() method with a predicate
IEnumerable<string> query1 = fruitClump.Where(fruit => fruit.Contains("o"));
// second: first call AsEnumerable() to hide Clump`s Where() method and thereby
// force System.Linq.Enumerable`s Where() method to be called.
IEnumerable<string> query2 =
fruitClump.AsEnumerable().Where(fruit => fruit.Contains("o"));6.Average
long ? [] longs = {null, 10007L, 37L, 399846234235L};
double ? average = longs.Average();
Console.WriteLine("The average is {0}.", average);7.Cast
System.Collections.ArrayList fruits2 = new System.Collections.ArrayList();
fruits2.Add("mongo");
fruits2.Add("apple");
fruits2.Add("lemon");
IEnumerable<string> query =
fruits2.Cast<string>().OrderBy(fruit => fruit).Select(fruit => fruit);
//下面的代码没有cast无法编译通过
// IEnumerable<string> query = fruits2.OrderBy(fruit => fruit).Select(fruit =>
// fruit);
foreach (string fruit in query) {
Console.WriteLine(fruit);
}8.Chunk 分块和分块并行
var list = Enumerable.Range(1, 100); // 1-100
var chunkSize = 10;
foreach (var chunk in list.Chunk(
chunkSize)) // 1-10,11-20,21-30,31-40,41-50,51-60...91-100
{
Console.WriteLine("=>");
foreach (var item in chunk) {
Console.WriteLine(item);
}
}
foreach (var chunk in list.Chunk(
chunkSize)) // 1-10,11-20,21-30,31-40,41-50,51-60...91-100
{
Console.WriteLine("=>");
Parallel.ForEach(chunk, (item) => { Console.WriteLine(item); });
}9.Concat
static Pet[] GetCats() {
Pet[] pets = {
new Pet{Name = "Barley", Age = 8},
new Pet{Name = "Boots", Age = 4},
new Pet{Name = "Whiskers", Age = 1},
};
return pets;
}
static Pet[] GetDogs() {
Pet[] pets = {
new Pet{Name = "Bounder", Age = 3},
new Pet{Name = "Snoopy", Age = 14},
new Pet{Name = "Fido", Age = 9},
};
return pets;
}Pet[] cats = GetCats();
Pet[] dogs = GetDogs();
IEnumerable<string> query =
cats.Select(cat => cat.Name).Concat(dogs.Select(dog => dog.Name));
foreach (string name in query) {
Console.WriteLine(name);
}10.Contains
long[] ls = new long[]{1L, 2L, 5L, 7L};
Console.WriteLine("is contains 5L: {0}", ls.Contains(5L));
Console.WriteLine("is contains 5L: {0}", Enumerable.Contains(ls, 5L));11.Count
long[] ls = new long[]{1, 2, 3, 4, 5, 6};
Console.WriteLine("count: {0}", ls.Count());
Console.WriteLine("count: {0}", Enumerable.Count(ls));12.DefaultIfEmpty
// non-empty sequence
List<Pet> pets = new List<Pet>{new Pet{Name = "Barley", Age = 8},
new Pet{Name = "Boots", Age = 4},
new Pet{Name = "Whiskers", Age = 1}};
foreach (Pet pet in pets.DefaultIfEmpty()) {
Console.WriteLine(pet.Name); // Barley Boots Whiskers
}
// empty sequence
List<int> numbers = new List<int>();
foreach (int number in numbers.DefaultIfEmpty()) {
Console.WriteLine(number); // 0
}13.Distinct 通过Comparer去重
Product[] products = new Product[]{new Product{Name = "apple", Code = 8},
new Product{Name = "apple", Code = 9},
new Product{Name = "orange", Code = 4},
new Product{Name = "apple", Code = 9},
new Product{Name = "lemon", Code = 12}};
foreach (Product product in products)
Console.WriteLine("name: {0}, code: {1}", product.Name, product.Code);
/*
* name: apple, code: 8
name: apple, code: 9
name: orange, code: 4
name: apple, code: 9
name: lemon, code: 12
*/
IEnumerable<Product> noduplicates = products.Distinct(new ProductComparer());
foreach (Product product in noduplicates)
Console.WriteLine("name: {0}, code: {1}", product.Name, product.Code);
/*
* name: apple, code: 8
name: apple, code: 9
name: orange, code: 4
name: lemon, code: 12
*/class ProductComparer : IEqualityComparer<Product> {
// Products are equal if their names and product number are equal.
public bool Equals(Product x, Product y) {
// check whether the compared objects reference the same data.
if (Object.ReferenceEquals(x, y)) return true;
// check whether any of the compared objects is null.
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
// check whether the products properties are equal.
return x.Code == y.Code && x.Name == y.Name;
}
// if Equals() returns true for a pair of objects
// then GetHashCode() must return the same value for these objects.
public int GetHashCode([ DisallowNull ] Product obj) {
// Check wheather the object is null
if (Object.ReferenceEquals(obj, null)) return 0;
// Get hash code for the Name field if it is not null
int hashProductName = obj.Name == null ? 0 : obj.Name.GetHashCode();
// Get hash code for the Code field
int hashProductCode = obj.Code.GetHashCode();
// Calculate the hash code for the product.
return hashProductName ^ hashProductCode;
}
}14.DistinctBy 通过func去重
Product[] collectionWithDuplicates = new Product[]{
new Product{Name = "good", Code = 9}, new Product{Name = "apple", Code = 9},
new Product{Name = "orange", Code = 4},
new Product{Name = "apple", Code = 9},
new Product{Name = "lemon", Code = 12}};
var uniqueCollection =
collectionWithDuplicates.DistinctBy(x => x.Name).ToList();
foreach (Product product in uniqueCollection)
Console.WriteLine("name: {0}, code: {1}", product.Name, product.Code);
/*
* name: good, code: 9
* name: orange, code: 5
name: apple, code: 9
name: lemon, code: 12
*/15.ElementAt
int[] ints = new int[]{
1, 2, 3, 4, 5,
};
Console.WriteLine(ints.ElementAt(3)); // 416.ElementAtOrDefault
int[] ints = new int[]{
1, 2, 3, 4, 5,
};
Console.WriteLine(ints.ElementAtOrDefault(5)); // 017.Empty 返回指定类型的空序列
IEnumerable<decimal> empty = Enumerable.Empty<decimal>();18.Except 产生两个序列的集合差
int[] ints1 = new int[]{
1, 2, 3, 4, 5,
};
int[] ints2 = new int[]{
1, 2, 0, 3, 6,
};
Console.WriteLine(JsonConvert.SerializeObject(
Enumerable.Except(ints1, ints2))); //[4,5] ints1中排除ints219.ExceptBy
Product[] products1 = new Product[]{new Product{Name = "blueberry", Code = 9},
new Product{Name = "apple", Code = 9},
new Product{Name = "orange", Code = 4},
new Product{Name = "apple", Code = 9},
new Product{Name = "lemon", Code = 12}};
Product[] products2 = new Product[]{new Product{Name = "mongo", Code = 9},
new Product{Name = "apple", Code = 9},
new Product{Name = "orange", Code = 4},
new Product{Name = "apple", Code = 9},
new Product{Name = "lemon", Code = 12}};
// Enumerable.ExceptBy(products1, products2, ProductNameSelector);
foreach (Product product in products1.ExceptBy(
products2.Select(ProductNameSelector),
ProductNameSelector)) // products.ExceptBy(names, NameSelector)
{
Console.WriteLine("name: {0}, code: {1}", product.Name,
product.Code); // name: blueberry, code: 9
}static string ProductNameSelector(Product product) => product.Name;20.First
int[] ints1 = new int[]{
1, 2, 3, 4, 5,
};
Console.WriteLine("first: {0}", ints1.First()); // 121.FirstOrDefault
int[] ints1 = new int[]{};
Console.WriteLine("first: {0}", ints1.FirstOrDefault()); // 022.GroupBy
// Create a list of pets.
List<Pet2> petsList = new List<Pet2>{new Pet2{Name = "Barley", Age = 8.3},
new Pet2{Name = "Boots", Age = 4.9},
new Pet2{Name = "Whiskers", Age = 1.5},
new Pet2{Name = "Daisy", Age = 4.3}};
// Group Pet.Age values by the Math.Floor of the age.
// Then project an anonymous type from each group
// that consists of the key, the count of the group's
// elements, and the minimum and maximum age in the group.
var query = petsList.GroupBy(
pet => Math.Floor(pet.Age), //@1
pet => pet.Age,
(baseAge, ages) =>
new {Key = baseAge, //@1
Count = ages.Count(), Min = ages.Min(), Max = ages.Max()});
Console.WriteLine(JsonConvert.SerializeObject(query));
// Iterate over each anonymous type.
foreach (var result in query) {
Console.WriteLine("\nAge group: " + result.Key);
Console.WriteLine("Number of pets in this age group: " + result.Count);
Console.WriteLine("Minimum age: " + result.Min);
Console.WriteLine("Maximum age: " + result.Max);
}
/* This code produces the following output:
Age group: 8
Number of pets in this age group: 1
Minimum age: 8.3
Maximum age: 8.3
Age group: 4
Number of pets in this age group: 2
Minimum age: 4.3
Maximum age: 4.9
Age group: 1
Number of pets in this age group: 1
Minimum age: 1.5
Maximum age: 1.5
*/23.IntersectBy
int[] ints1 = new int[]{
1, 2, 3, 4, 5,
};
int[] ints2 = new int[]{
1, 2, 0, 3, 6,
};
Console.WriteLine(
JsonConvert.SerializeObject(Enumerable.Intersect(ints1, ints2))); //[1,2,3]
Product[] products1 = new Product[]{new Product{Name = "blueberry", Code = 9},
new Product{Name = "apple", Code = 9},
new Product{Name = "orange", Code = 4},
new Product{Name = "apple", Code = 9},
new Product{Name = "lemon", Code = 12}};
Product[] products2 = new Product[]{new Product{Name = "mongo", Code = 9},
new Product{Name = "apple", Code = 9},
new Product{Name = "orange", Code = 4},
new Product{Name = "apple", Code = 9},
new Product{Name = "lemon", Code = 12}};
Console.WriteLine(JsonConvert.SerializeObject(
Enumerable.Intersect(products1, products2, new ProductComparer())));
//[{"Name":"apple","Code":9},{"Name":"orange","Code":4},{"Name":"lemon","Code":12}]24.Join
Person3 magnus = new Person3{Name = "Hedlund, Magnus"};
Person3 terry = new Person3{Name = "Adams, Terry"};
Person3 charlotte = new Person3{Name = "Weiss, Charlotte"};
Pet3 barley = new Pet3{Name = "Barley", Owner = terry};
Pet3 boots = new Pet3{Name = "Boots", Owner = terry};
Pet3 whiskers = new Pet3{Name = "Whiskers", Owner = charlotte};
Pet3 daisy = new Pet3{Name = "Daisy", Owner = magnus};
List<Person3> people3 = new List<Person3>{magnus, terry, charlotte};
List<Pet3> pets3 = new List<Pet3>{barley, boots, whiskers, daisy};
// create a list of person-pet pairs where
// each element is an anonymous type that contains a
// pet`s name and the name of the person that owns the pet
// Join<TOuter,TInner,TKey,TResult>(IEnumerable<TOuter>, IEnumerable<TInner>,
// Func<TOuter,TKey>, Func<TInner,TKey>, Func<TOuter,TInner,TResult>)
var query = people3.Join(
pets3, person => person, pet => pet.Owner,
(person, pet) => new {OwnerName = person.Name, Pet = pet.Name});
foreach (var obj in query) {
Console.WriteLine("{0} - {1}", obj.OwnerName, obj.Pet);
}25.Last
var a = new string[] { "123", "123", "123", "333" };
Console.WriteLine(a.Last());//33326.LastOrDefault
var a = new string[] { };
Console.WriteLine(a.LastOrDefault());// 27.LongCount
Pet[] pets = {
new Pet{Name = “Barley”, Age = 8},
new Pet{Name = “Boots”, Age = 4},
new Pet{Name = “Whiskers”, Age = 1},
};
const int Age = 3;
long count = pets.LongCount(pet => pet.Age > Age);
Console.WriteLine(“There are {0} animals over age {1}.”, count, Age);
28.Max
var a = new int[] { 1, 3, 2 };
Console.WriteLine("the max: {0}", a.Max());29.MaxBy
Pet[] pets = {
new Pet{Name = "Barley", Age = 8},
new Pet{Name = "Boots", Age = 4},
new Pet{Name = "Whiskers", Age = 1},
};
Console.WriteLine("the max: {0}",
JsonConvert.SerializeObject(pets.MaxBy(pet => pet.Age)));
Console.WriteLine("the max: {0}",
JsonConvert.SerializeObject(pets.MaxBy(pet => pet,
new MyPetComparer())));public class MyPetComparer : IComparer<Pet> {
int IComparer<Pet>.Compare(Pet? x, Pet? y) { return x.Age - y.Age; }
}30.Min
var a = new int[] { 1, 3, 2 };
Console.WriteLine("the min: {0}", a.Min());31.MinBy
Pet[] pets = {
new Pet{Name = "Barley", Age = 8},
new Pet{Name = "Boots", Age = 4},
new Pet{Name = "Whiskers", Age = 1},
};
Console.WriteLine("the min: {0}",
JsonConvert.SerializeObject(pets.MinBy(pet => pet.Age)));
Console.WriteLine("the min: {0}",
JsonConvert.SerializeObject(pets.MinBy(pet => pet,
new MyPetComparer())));public class MyPetComparer : IComparer<Pet> {
int IComparer<Pet>.Compare(Pet? x, Pet? y) { return x.Age - y.Age; }
}32.OfType
ArrayList mixedList = new ArrayList();
mixedList.Add(0);
mixedList.Add("Gnanavel Sekar");
mixedList.Add("Two");
mixedList.Add(3);
mixedList.Add(3.21f);
mixedList.Add(new Pet{Name = "Whiskers", Age = 1});
var stringResult = from s in mixedList.OfType<string>() select s;
foreach (var item in stringResult) {
Console.WriteLine(item);
}
/*
* Gnanavel Sekar
* Two
*/
var intResult = from s in mixedList.OfType<int>() select s;
foreach (var item in intResult) {
Console.WriteLine(item);
}
/*
* 0
* 3
*/33.OrderBy 升序
Pet[] pets = {
new Pet{Name = "Barley", Age = 8},
new Pet{Name = "Boots", Age = 4},
new Pet{Name = "Whiskers", Age = 1},
};
Console.WriteLine(JsonConvert.SerializeObject(pets.OrderBy(pet => pet.Age)));
Console.WriteLine(
JsonConvert.SerializeObject(pets.OrderBy(pet => pet, new MyPetComparer())));public class MyPetComparer : IComparer<Pet> {
int IComparer<Pet>.Compare(Pet? x, Pet? y) { return x.Age - y.Age; }
}34.OrderByDescending 降序
Pet[] pets = {
new Pet{Name = "Barley", Age = 8},
new Pet{Name = "Boots", Age = 4},
new Pet{Name = "Whiskers", Age = 1},
};
Console.WriteLine(
JsonConvert.SerializeObject(pets.OrderByDescending(pet => pet.Age)));
Console.WriteLine(JsonConvert.SerializeObject(
pets.OrderByDescending(pet => pet, new MyPetComparer())));public class MyPetComparer : IComparer<Pet> {
int IComparer<Pet>.Compare(Pet? x, Pet? y) { return x.Age - y.Age; }
}35.Prepend 向前追加
List<int> numbers = new List<int>{1, 2, 3, 4};
numbers.Prepend(0);
Console.WriteLine(JsonConvert.SerializeObject(numbers)); // 1,2,3,4
Console.WriteLine(JsonConvert.SerializeObject(numbers.Prepend(0))); // 0,1,2,3,4
List<int> newNumbers = numbers.Prepend(0).ToList();
Console.WriteLine(JsonConvert.SerializeObject(newNumbers)); // 0,1,2,3,436.Range
IEnumerable<int> squares = Enumerable.Range(1, 10).Select(x => x * x);
foreach (int num in squares) {
Console.WriteLine(num);
}37.Repeat 生成多个相同重复值的序列
IEnumerable<string> strs = Enumerable.Repeat("I like programming.", 15);
foreach (String str in strs) {
Console.WriteLine(str);
}38.Reverse
List<int> numbers = new List<int>{1, 2, 3, 4};
numbers.Reverse();
Console.WriteLine(JsonConvert.SerializeObject(numbers)); // 4,3,2,139.Select
string[] fruits3 = {"apple", "banana", "mango",
"orange", "passionfruit", "grape"};
var query = fruits3.Select((fruit, index) =>
new {index, str = fruit.Substring(0, index)});
foreach (var obj in query) {
Console.WriteLine("{0}", obj);
}40.SelectMany
PetOwner[] petOwners = new PetOwner[]{
new PetOwner{Name = "Higa", Pets = new List<string>{"Scruffy", "Sam"}},
new PetOwner{Name = "Ashkenazi",
Pets = new List<string>{"Walker", "Sugar"}},
new PetOwner{Name = "Price",
Pets = new List<string>{"Scratches", "Diesel"}},
new PetOwner{Name = "Hines", Pets = new List<string>{"Dusty"}},
};
var query1 = petOwners.SelectMany(
petOwner => petOwner.Pets,
(petOwner, petName) => new {petOwner, petName}); //将petOwner.Pets展开
Console.WriteLine(JsonConvert.SerializeObject(query1));
/*
* [
* {"petOwner":{"Name":"Higa","Pets":["Scruffy","Sam"]},"petName":"Scruffy"},
* {"petOwner":{"Name":"Higa","Pets":["Scruffy","Sam"]},"petName":"Sam"},
* {"petOwner":{"Name":"Ashkenazi","Pets":["Walker","Sugar"]},"petName":"Walker"},
* {"petOwner":{"Name":"Ashkenazi","Pets":["Walker","Sugar"]},"petName":"Sugar"},
* {"petOwner":{"Name":"Price","Pets":["Scratches","Diesel"]},"petName":"Scratches"},
* {"petOwner":{"Name":"Price","Pets":["Scratches","Diesel"]},"petName":"Diesel"},
* {"petOwner":{"Name":"Hines","Pets":["Dusty"]},"petName":"Dusty"}
* ]
*/
// project the pet owner`s name and the pet`s name
var query = petOwners
.SelectMany(petOwner => petOwner.Pets,
(petOwner, petName) => new {petOwner, petName})
.Where(ownerAndPet => ownerAndPet.petName.StartsWith("S"))
.Select(ownerAndPet => new {Owner = ownerAndPet.petOwner.Name,
Pet = ownerAndPet.petName});
foreach (var obj in query) {
Console.WriteLine(obj);
}41.SequenceEqual
Pet pet1 = new Pet{Name = "Turbo", Age = 2};
Pet pet2 = new Pet{Name = "Peanut", Age = 9};
List<Pet> pets1 = new List<Pet>{pet1, pet2};
List<Pet> pets2 = new List<Pet>{pet1, pet2};
bool equal = pets1.SequenceEqual(pets2);
Console.WriteLine("The sequence is equals: {0}.", equal); // True
List<Pet> pets3 = new List<Pet>{pet1, pet2};
List<Pet> pets4 = new List<Pet>{
new Pet{Name = "Turbo", Age = 2},
new Pet{Name = "Peanut", Age = 9},
};
bool equal2 = pets3.SequenceEqual(pets4);
Console.WriteLine("The sequence is equals: {0}.", equal2); // False
//在这里比较的是引用地址
//可以自行实现IEquatable接口，重写GetHashCode和Equals方法
List<ProductA> pets5 = new List<ProductA>{
new ProductA{Name = "Turbo", Code = 2},
new ProductA{Name = "Peanut", Code = 9},
};
List<ProductA> pets6 = new List<ProductA>{
new ProductA{Name = "Turbo", Code = 2},
new ProductA{Name = "Peanut", Code = 9},
};
bool equal3 = pets5.SequenceEqual(pets6);
Console.WriteLine("The sequence is equals: {0}.", equal3); // True
Console.WriteLine(JsonConvert.SerializeObject((9, 9))); //{"Item1":9,"Item2":9}public class ProductA : IEquatable<ProductA> {
public string Name {
get;
set;
}
public int Code {
get;
set;
}
public bool Equals(ProductA other) {
if (other is null) return false;
return this.Name == other.Name && this.Code == other.Code;
}
public override bool Equals(object obj) => Equals(obj as ProductA);
public override int GetHashCode() =>(Name, Code).GetHashCode();
}42.Single 返回一条匹配结果
string[] fruits3 = {"apple", "banana", "mango",
"orange", "passionfruit", "grape"};
string fruit1 = null;
try {
fruit1 = fruits3.Single(fruit => fruit.Length > 20);
} catch (System.InvalidOperationException) {
Console.WriteLine(
@"The collection does not contain exactly one element whose length is grater than 20.");
}
Console.WriteLine(fruit1);43.SingleOrDefault
string[] fruits3 = {"apple", "banana", "mango",
"orange", "passionfruit", "grape"};
string fruit1 = fruits3.SingleOrDefault(fruit => fruit.Length > 20);
Console.WriteLine(fruit1);44.Skip 从序号0开始跳过指定个
int[] grades = {59, 82, 70, 56, 92, 98, 85};
IEnumerable<int> lowerGrades = grades.OrderByDescending(g => g).Skip(3);
Console.WriteLine("All grades except the top three are:");
foreach (int grade in lowerGrades) {
Console.WriteLine(grade);
} /*
* All grades except the top three are:
82
70
59
56
*/45.SkipLast 从末尾倒数跳过指定个
int[] grades = {59, 82, 70, 56, 92, 98, 85};
IEnumerable<int> lowerGrades = grades.OrderByDescending(g => g).SkipLast(3);
Console.WriteLine("All grades except the last three are:");
foreach (int grade in lowerGrades) {
Console.WriteLine(grade);
} /*
*98
92
85
82
*/46.SkipWhile 按特定条件
int[] grades = {59, 82, 70, 56, 92, 98, 85};
IEnumerable<int> lowerGrades =
grades.OrderByDescending(g => g).SkipWhile(g => g >= 80);
Console.WriteLine("All grades below 80:");
foreach (int grade in lowerGrades) {
Console.WriteLine(grade);
} /*
*All grades below 80:
*70
*59
*56
*/47.Sum 求和
int[] grades = { 59, 82, 70, 56, 92, 98, 85 };
Console.WriteLine("sum: {0}", grades.Sum());//sum: 54248.Take 从序号0开始选择指定个
int[] grades = {59, 82, 70, 56, 92, 98, 85};
IEnumerable<int> lowerGrades = grades.OrderByDescending(g => g).Take(3);
Console.WriteLine("the top threee grades are:");
foreach (int grade in lowerGrades) {
Console.WriteLine(grade);
} /*
98
92
85
*/49.TakeLast 从末尾开始倒数选择指定个
int[] grades = {59, 82, 70, 56, 92, 98, 85};
IEnumerable<int> lowerGrades = grades.OrderByDescending(g => g).TakeLast(3);
Console.WriteLine("the last three grades are:");
foreach (int grade in lowerGrades) {
Console.WriteLine(grade);
}50.TakeWhile 按特定条件选择
int[] grades = {59, 82, 70, 56, 92, 98, 85};
IEnumerable<int> lowerGrades =
grades.OrderByDescending(g => g).TakeWhile(g => g >= 80);
Console.WriteLine("All grades grater than 80:");
foreach (int grade in lowerGrades) {
Console.WriteLine(grade);
}51.ThenBy 后续排序，用于OrderBy后
string[] fruits3 = {"grape", "passionfruit", "banana", "mango",
"orange", "raspberry", "apple", "blueberry"};
// Sort the strings first by their length and then
// alphabetically by passing the identity selector function.
IEnumerable<string> query =
fruits3.OrderBy(fruit => fruit.Length).ThenBy(fruit => fruit);
foreach (string fruit in query) {
Console.WriteLine(fruit);
}
/*
* apple
* grape
* mango
* banana
* orange
* blueberry
* raspberry
* passionfruit
*/
//当没有使用ThenBy时，注意观察字符长度一致的排序
/* grape
* mango
* apple
* banana
* orange
* raspberry
* blueberry
* passionfruit
*/52.ThenByDescending 后续排序倒序
string[] fruits3 = {"apPLe", "baNanA", "apple", "APple",
"orange", "BAnana", "ORANGE", "apPLE"};
// Sort the strings first ascending by their length and
// then descending using a custom case insensitive comparer.
IEnumerable<string> query =
fruits3.OrderBy(fruit => fruit.Length)
.ThenByDescending(fruit => fruit, new CaseInsensitiveComparer());
foreach (string fruit in query) {
Console.WriteLine(fruit);
}
//无ThenByDescending时，注意观察长度一致的单词排序
/*
* apPLe
* apple
* APple
* apPLE
* baNanA
* orange
* BAnana
* ORANGE
*/
//有ThenByDescending时，注意观察长度一致的单词排序
/*
* apPLe
* apple
* APple
* apPLE
* orange
* ORANGE
* baNanA
* BAnana
*/53.ToArray
List<Package> packages = new List<Package>{
new Package{Company = "Coho Vineyard", Weight = 25.2},
new Package{Company = "Lucerne Publishing", Weight = 18.7},
new Package{Company = "Wingtip Toys", Weight = 6.0},
new Package{Company = "Adventure Works", Weight = 33.8}};
string[] companies = packages.Select(pkg => pkg.Company).ToArray();
foreach (string company in companies) {
Console.WriteLine(company);
}
/*
*Coho Vineyard
*Lucerne Publishing
*Wingtip Toys
*Adventure Works
*/54.ToDirectory
List<Package> packages =
new List<Package>{new Package{Company = "Coho Vineyard", Weight = 25.2,
TrackingNumber = 89453312L},
new Package{Company = "Lucerne Publishing",
Weight = 18.7, TrackingNumber = 89112755L},
new Package{Company = "Wingtip Toys", Weight = 6.0,
TrackingNumber = 299456122L},
new Package{Company = "Adventure Works", Weight = 33.8,
TrackingNumber = 4665518773L}};
// Create a Dictionary of Package objects,
// using TrackingNumber as the key.
Dictionary<long, Package> dictionary =
packages.ToDictionary(p => p.TrackingNumber);
foreach (KeyValuePair<long, Package> kvp in dictionary) {
Console.WriteLine("Key {0}: {1}, {2} pounds", kvp.Key, kvp.Value.Company,
kvp.Value.Weight);
}class Package {
public string Company {
get;
set;
}
public double Weight {
get;
set;
}
public long TrackingNumber {
get;
set;
}
}55.ToHashSet
public class ProductA : IEquatable<ProductA> {
public string Name {
get;
set;
}
public int Code {
get;
set;
}
public bool Equals(ProductA other) {
if (other is null) return false;
return this.Name == other.Name && this.Code == other.Code;
}
public override bool Equals(object obj) => Equals(obj as ProductA);
public override int GetHashCode() =>(Name, Code).GetHashCode();
}
public class ProductB {
public string Name {
get;
set;
}
public int Code {
get;
set;
}
}int[] a = new int[]{1, 2, 3, 4, 5, 4, 3, 2, 1};
Console.WriteLine(JsonConvert.SerializeObject(a.ToHashSet())); //[1,2,3,4,5]
List<ProductA> pets5 = new List<ProductA>{
new ProductA{Name = "Peanut", Code = 9},
new ProductA{Name = "Turbo", Code = 2},
new ProductA{Name = "Peanut", Code = 9},
};
Console.WriteLine(JsonConvert.SerializeObject(
pets5
.ToHashSet())); //[{"Name":"Peanut","Code":9},{"Name":"Turbo","Code":2}]
List<ProductB> pets6 = new List<ProductA2>{
new ProductB{Name = "Peanut", Code = 9},
new ProductB{Name = "Turbo", Code = 2},
new ProductB{Name = "Peanut", Code = 9},
};
Console.WriteLine(JsonConvert.SerializeObject(pets6.ToHashSet(
new ProductBComparer()))); //[{"Name":"Peanut","Code":9},{"Name":"Turbo","Code":2}]public class ProductBComparer : IEqualityComparer<Product> {
bool IEqualityComparer<ProductB>.Equals(ProductB? x, ProductB? y) {
if (x is null || y is null) return false;
return x.Name == y.Name && x.Code == y.Code;
}
int IEqualityComparer<ProductB>.GetHashCode(ProductB obj) {
return (obj.Name, obj.Code).GetHashCode();
}
}56.ToList
int[] a = new int[]{1, 2, 3, 4, 5, 4, 3, 2, 1};
Console.WriteLine(
JsonConvert.SerializeObject(a.ToList())); //[1,2,3,4,5,4,3,2,1]57.ToLookup 分组
class PackageB {
public string Company {
get;
set;
}
public double Weight {
get;
set;
}
public long TrackingNumber {
get;
set;
}
}// Create a list of Packages.
List<PackageB> packages = new List<PackageB>{
new PackageB{Company = "Coho Vineyard", Weight = 25.2,
TrackingNumber = 89453312L},
new PackageB{Company = "Lucerne Publishing", Weight = 18.7,
TrackingNumber = 89112755L},
new PackageB{Company = "Wingtip Toys", Weight = 6.0,
TrackingNumber = 299456122L},
new PackageB{Company = "Contoso Pharmaceuticals", Weight = 9.3,
TrackingNumber = 670053128L},
new PackageB{Company = "Wide World Importers", Weight = 33.8,
TrackingNumber = 4665518773L}};
// Create a Lookup to organize the packages.
// Use the first character of Company as the key value.
// Select Company appended to TrackingNumber
// as the element values of the Lookup.
ILookup<char, string> lookup = packages.ToLookup(
p => p.Company[0], p => p.Company + " " + p.TrackingNumber);
// Iterate through each IGrouping in the Lookup.
foreach (IGrouping<char, string> packageGroup in lookup) {
// Print the key value of the IGrouping.
Console.WriteLine(packageGroup.Key);
// Iterate through each value in the
// IGrouping and print its value.
foreach (string str in packageGroup) Console.WriteLine(" {0}", str);
}
/*
*
C
Coho Vineyard 89453312
Contoso Pharmaceuticals 670053128
L
Lucerne Publishing 89112755
W
Wingtip Toys 299456122
Wide World Importers 4665518773*/58.TryGetNonEnumeratedCount 尝试在不枚举的情况下获取序列中元素数量
int[] a = new int[]{1, 2, 3, 4, 5, 4, 3, 2, 1};
a.TryGetNonEnumeratedCount(out int theCount);
Console.WriteLine(theCount); // 959.Union 联合（会去重）
public class ProductA : IEquatable<ProductA> {
public string Name {
get;
set;
}
public int Code {
get;
set;
}
public bool Equals(ProductA other) {
if (other is null) return false;
return this.Name == other.Name && this.Code == other.Code;
}
public override bool Equals(object obj) => Equals(obj as ProductA);
public override int GetHashCode() =>(Name, Code).GetHashCode();
}int[] ints1 = {5, 3, 9, 7, 5, 9, 3, 7};
int[] ints2 = {8, 3, 6, 4, 4, 9, 1, 0};
IEnumerable<int> union
= ints1.Union(ints2);
foreach (int num in union) {
Console.Write("{0} ", num); // 5 3 9 7 8 6 4 1 0
}
Console.WriteLine();
ProductA[] store1 = {new ProductA{Name = "apple", Code = 9},
new ProductA{Name = "orange", Code = 4}};
ProductA[] store2 = {new ProductA{Name = "apple", Code = 9},
new ProductA{Name = "lemon", Code = 12}};
IEnumerable<ProductA> union2 = store1.Union(store2);
Console.WriteLine(JsonConvert.SerializeObject(
union2)); //[{"Name":"apple","Code":9},{"Name":"orange","Code":4},{"Name":"lemon","Code":12}]60.UnionBy 将函数处理后的结果联合
var a = new[]{1, 2, 3, 4, 5, 6, 7};
var b = new[]{4, 5, 6, 7, 8, 9, 10};
Func<int, string> transform = i => i.ToString();
var result = a.UnionBy(b, transform);
Console.WriteLine(JsonConvert.SerializeObject(
result)); //"1", "2", "3", "4", "5", "6", "7", "8", "9", "10"61.Where
List<string> fruits2 =
new List<string>{"apple", "passionfruit", "banana", "mango",
"orange", "blueberry", "grape", "strawberry"};
IEnumerable<string> query = fruits2.Where(fruit => fruit.Length < 6);
foreach (string fruit in query) {
Console.WriteLine(fruit);
}
// apple mango grape62.Zip 结合两个集合
int[] numbers = {1, 2, 3, 4};
string[] words = {"one", "two", "three"};
var numbersAndWords =
numbers.Zip(words, (first, second) => first + " " + second);
foreach (var item in numbersAndWords) Console.WriteLine(item);
/*
* 1 one
* 2 two
* 3 three
*/