常见Linq表达式示例
当我编写代码时，我开始确定可以使用Linq的地方。 我的问题是我对语法还很新。 我通过例子学到了最好的东西，但我似乎无法轻易找到我需要的例子。
我想开始这个线程来创建一个常见的Linq表达式的存储库，其他人可能会通过谷歌偶然发现。
问题：您能提供用于常见任务的Linq表达式的任何示例吗？
例如，我已经写了以下内容：
- 搜索列表
- 总结一个数组
- 总结元素集合中的某个属性
为了启动线程，我将发布包含这些内容的答案。
枚举列表以查找某个元素
tboShippingLotNumber existingLotNumber = (tboShippingLotNumber)(from lot in shipmentDetailLine.LotNumbers where (lot.LotNumber == lotNumber) && (lot.ShipLineKey == shipmentDetailLine.Key) select lot).ElementAtOrDefault(0); if (existingLotNumber == null) { // not found exception }
总结一个数组：
decimal[] array = { 1.5m, 2.5m, 3.5m }; decimal sum = array.Sum();
在对象列表中对某个属性求和
decimal sum = (from shipment in _ShipmentData.Shipments select shipment.AmountShipped).Sum()
涵盖了Linq的大多数例子
using System; using System.Linq; using System.Collections.Generic; namespace LinqExamples { // https://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b class Program { static void Main(string[] args) { loadData(); // Print all the subjects Console.WriteLine("------------------(SelectMany) Print all the subjects--------------------"); Console.WriteLine(string.Join("\n", students.SelectMany(s => s.subjects).Distinct())); // Sort by first subject and then by first name Console.WriteLine("\n------------------(OrderBy ThenBy) Sort by first subject and then by first name--------------------"); Console.WriteLine(string.Join("\n", students.OrderBy(x => x.subjects[0]).ThenBy(m => m.FirstName))); Console.WriteLine("\n------------------Group by first subject and then no of student oppted for the subject--------------------"); Console.WriteLine(string.Join("\n", students.GroupBy(x => x.subjects[0]).Select(s => new { Subject = s.Key, count = s.Count() }))); foreach (var g in students.GroupBy(x => x.subjects[0]).Select(s => new { Subject = s.Key, count = s.Count(), studentFirstName = s.Select(x => x.FirstName) })) { Console.WriteLine("Subject: {0}, Total Student: {1}, Student FirstNames: {2}", g.Subject, g.count, string.Join(", ", g.studentFirstName)); } string wordsString = "This is the same book which all the student used to read"; Console.WriteLine(string.Join("\n", wordsString.Split(' ').GroupBy(x => x).Select(s => new { Word = s.Key, count = s.Count() }))); Console.WriteLine("\n------------------(OrderByDescending) Top 2 Salary--------------------"); Console.WriteLine(string.Join("\n", students.OrderByDescending(s => s.Salary).Take(2))); Console.WriteLine("\n------------------Distinct--------------------"); int[] arr = { 2, 2, 3, 5, 5 }; Console.WriteLine($"[{string.Join(", ", arr)}]"); Console.WriteLine(string.Join(", ", arr.Distinct())); Console.WriteLine("\n------------------(Union) Unique numbers from both arrays--------------------"); int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; int[] numbersB = { 1, 3, 5, 7, 8 }; Console.WriteLine($"[{string.Join(", ", numbersA)}]"); Console.WriteLine($"[{string.Join(", ", numbersB)}]"); Console.WriteLine(string.Join(", ", numbersA.Union(numbersB).OrderBy(x => x))); Console.WriteLine("\n------------------(Intersect) Common numbers shared by both arrays--------------------"); Console.WriteLine($"[{string.Join(", ", numbersA)}]"); Console.WriteLine($"[{string.Join(", ", numbersB)}]"); Console.WriteLine(string.Join(", ", numbersA.Intersect(numbersB).OrderBy(x => x))); Console.WriteLine("\n------------------(Except) Numbers in first array but not second array--------------------"); Console.WriteLine($"[{string.Join(", ", numbersA)}]"); Console.WriteLine($"[{string.Join(", ", numbersB)}]"); Console.WriteLine(string.Join(", ", numbersA.Except(numbersB).OrderBy(x => x))); Console.WriteLine("\n------------------Concat numbers from both arrays--------------------"); Console.WriteLine($"[{string.Join(", ", numbersA)}]"); Console.WriteLine($"[{string.Join(", ", numbersB)}]"); Console.WriteLine(string.Join(", ", numbersA.Concat(numbersB).OrderBy(x => x))); Console.WriteLine("\n------------------ToDictionary--------------------"); var scoreRecords = new[] { new {Name = "Alice", Score = 50}, new {Name = "Bob" , Score = 40}, new {Name = "Cathy", Score = 45} }; var scoreRecordsDict = scoreRecords.ToDictionary(sr => sr.Name); Console.WriteLine("Bob's score: {0}", scoreRecordsDict["Bob"]); Console.WriteLine("\n------------------OfType--------------------"); object[] numbers = { null, 1.0, "two", 3, "four", 5, "six", 7.0, true }; Console.WriteLine($"[{string.Join(", ", numbers)}]"); var doubles = numbers.OfType(); Console.WriteLine("Numbers stored as doubles: " + string.Join(", ", numbers.OfType ())); Console.WriteLine("Numbers stored as bool: " + string.Join(", ", numbers.OfType())); Console.WriteLine("Numbers stored as string: " + string.Join(", ", numbers.OfType())); Console.WriteLine("Numbers stored as int: " + string.Join(", ", numbers.OfType())); Console.WriteLine("\n------------------First with Condition--------------------"); string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; Console.WriteLine($"[{string.Join(", ", strings)}]"); Console.WriteLine("A string starting with 'o': {0}", strings.FirstOrDefault(s => s[0] == 'o')); Console.WriteLine("\n------------------GroupBy with Condition--------------------"); int[] num = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; Console.WriteLine($"[{string.Join(", ", num)}]"); var numberGroups = num.GroupBy(x => x % 5).Select(g => new { Remainder = g.Key, Numbers = g }); foreach (var g in numberGroups) { Console.WriteLine("Numbers with a remainder of {0} when divided by 5: {1}", g.Remainder, string.Join(", ", g.Numbers)); } Console.WriteLine("\n------------------Range--------------------"); Console.WriteLine(string.Join(", ", Enumerable.Range(1, 5))); Console.WriteLine($"\n{string.Join("", Enumerable.Repeat('-', 18))}Repeat{string.Join("", Enumerable.Repeat('-', 18))}"); Console.WriteLine("Repeat(Print) '*' for 5 times: " + string.Join("", Enumerable.Repeat('*', 5))); Console.WriteLine("\n------------------Any--------------------"); string[] words = { "believe", "relief", "receipt", "field" }; Console.WriteLine($"[{string.Join(", ", words)}]"); Console.WriteLine("Is there any word which contains 'ei': {0}", words.Any(w => w.Contains("ei"))); Console.WriteLine("Is there any word which start with 'f': {0}", words.Any(w => w[0] == 'f')); Console.WriteLine("Is there any word which start with 'n': {0}", words.Any(w => w[0] == 'n')); Console.WriteLine("\n------------------All--------------------"); int[] nos = { 1, 11, 3, 19, 41, 65, 19 }; Console.WriteLine($"[{string.Join(", ", nos)}]"); Console.WriteLine("The list contains only odd numbers: {0}", nos.All(n => n % 2 == 1)); Console.WriteLine("The list contains only even numbers: {0}", nos.All(n => n % 2 == 0)); Console.WriteLine("\n------------------Where with index --------------------"); string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; Console.WriteLine($"[{string.Join(", ", digits)}]"); var shortDigits = digits.Where((digit, index) => digit.Length < index); Console.WriteLine(string.Join(" is shorter in length than its index position\n", shortDigits)); Console.WriteLine("\n------------------Select with index --------------------"); Console.WriteLine($"[{string.Join(", ", digits)}]"); foreach (var n in digits.Select((x, indexi) => new { word = x, InPlace = indexi })) { Console.WriteLine("{0}: {1}", n.word, n.InPlace); } Console.WriteLine("\n------------------SequenceEqual (all array element matches in the same order)--------------------"); var wordsA = new string[] { "cherry", "apple", "blueberry" }; var wordsB = new string[] { "cherry", "apple", "blueberry" }; Console.WriteLine($"[{string.Join(", ", wordsA)}]"); Console.WriteLine($"[{string.Join(", ", wordsB)}]"); Console.WriteLine("The sequences match: {0}", wordsA.SequenceEqual(wordsB)); } private static void loadData() { students.Add(new Student("English", "Math")); students.Add(new Student("Physics", "Math")); students.Add(new Student("Chemistry", "Math")); students.Add(new Student("English", "Hindi")); students.Add(new Student("GK", "Science")); students.Add(new Student("English", "Math")); students.Add(new Student("Physics", "Math")); students.Add(new Student("Chemistry", "Math")); students.Add(new Student("English", "Hindi")); students.Add(new Student("GK", "Science")); } public static List students = new List (); } public class Student { public string FirstName { get; set; } = Faker.Name.First(); public string LastName { get; set; } = Faker.Name.Last(); public string Mobile { get; set; } = Faker.Phone.Number(); public int Salary { get; set; } = Faker.RandomNumber.Next(1000, 10000); public Guid Id { get; set; } = Guid.NewGuid(); public List subjects = new List (); public Student(params string[] subjects) { foreach (var sub in subjects) { this.subjects.Add(sub); } } public override string ToString() { return $"{this.FirstName} {this.LastName} {this.Salary}\t{this.subjects[0]}, {this.subjects[1]} {this.Mobile}"; } } }