101个LINQ示例，包含几乎全部操作
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Restriction Operators Where - Simple 1 public void Linq1() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var lowNums = from n in numbers where n < 5 select n; Console.WriteLine("Numbers < 5:"); foreach (var x in lowNums) { Console.WriteLine(x); } } Where - Simple 2 public void Linq2() { List products = GetProductList(); var soldOutProducts = from p in products where p.UnitsInStock == 0 select p; Console.WriteLine("Sold out products:"); foreach (var product in soldOutProducts) { Console.WriteLine("{0} is sold out!", product.ProductName); } } Where - Simple 3 public void Linq3() { List products = GetProductList(); var expensiveInStockProducts = from p in products where p.UnitsInStock > 0 && p.UnitPrice > 3.00M select p; Console.WriteLine("In-stock products that cost more than 3.00:"); foreach (var product in expensiveInStockProducts) { Console.WriteLine("{0} is in stock and costs more than 3.00.", product.ProductName); } } Where - Drilldown public void Linq4() { List customers = GetCustomerList(); var waCustomers = from c in customers where c.Region == "WA" select c; Console.WriteLine("Customers from Washington and their orders:"); foreach (var customer in waCustomers) { Console.WriteLine("Customer {0}: {1}", customer.CustomerID, customer.CompanyName); foreach (var order in customer.Orders) { Console.WriteLine(" Order {0}: {1}", order.OrderID, order.OrderDate); } } } Where - Indexed public void Linq5() { string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; var shortDigits = digits.Where((digit, index) => digit.Length < index); Console.WriteLine("Short digits:"); foreach (var d in shortDigits) { Console.WriteLine("The word {0} is shorter than its value.", d); } } Projection Operators Select - Simple 1 public void Linq6() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var numsPlusOne = from n in numbers select n + 1; Console.WriteLine("Numbers + 1:"); foreach (var i in numsPlusOne) { Console.WriteLine(i); } } Select - Simple 2 public void Linq7() { List products = GetProductList(); var productNames = from p in products select p.ProductName; Console.WriteLine("Product Names:"); foreach (var productName in productNames) { Console.WriteLine(productName); } } Select - Transformation public void Linq8() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; var textNums = from n in numbers select strings[n]; Console.WriteLine("Number strings:"); foreach (var s in textNums) { Console.WriteLine(s); } } Select - Anonymous Types 1 public void Linq9() { string[] words = { "aPPLE", "BlUeBeRrY", "cHeRry" }; var upperLowerWords = from w in words select new {Upper = w.ToUpper(), Lower = w.ToLower()}; foreach (var ul in upperLowerWords) { Console.WriteLine("Uppercase: {0}, Lowercase: {1}", ul.Upper, ul.Lower); } } Select - Anonymous Types 2 public void Linq10() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; var digitOddEvens = from n in numbers select new {Digit = strings[n], Even = (n % 2 == 0)}; foreach (var d in digitOddEvens) { Console.WriteLine("The digit {0} is {1}.", d.Digit, d.Even ? "even" : "odd"); } } Select - Anonymous Types 3 public void Linq11() { List products = GetProductList(); var productInfos = from p in products select new {p.ProductName, p.Category, Price = p.UnitPrice}; Console.WriteLine("Product Info:"); foreach (var productInfo in productInfos) { Console.WriteLine("{0} is in the category {1} and costs {2} per unit.", productInfo.ProductName, productInfo.Category, productInfo.Price); } } Select - Indexed public void Linq12() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var numsInPlace = numbers.Select((num, index) => new {Num = num, InPlace = (num == index)}); Console.WriteLine("Number: In-place?"); foreach (var n in numsInPlace) { Console.WriteLine("{0}: {1}", n.Num, n.InPlace); } } Select - Filtered public void Linq13() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; var lowNums = from n in numbers where n < 5 select digits[n]; Console.WriteLine("Numbers < 5:"); foreach (var num in lowNums) { Console.WriteLine(num); } } SelectMany - Compound from 1 public void Linq14() { int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; int[] numbersB = { 1, 3, 5, 7, 8 }; var pairs = from a in numbersA, b in numbersB where a < b select new {a, b}; Console.WriteLine("Pairs where a < b:"); foreach (var pair in pairs) { Console.WriteLine("{0} is less than {1}", pair.a, pair.b); } } SelectMany - Compound from 2 public void Linq15() { List customers = GetCustomerList(); var orders = from c in customers, o in c.Orders where o.Total < 500.00M select new {c.CustomerID, o.OrderID, o.Total}; ObjectDumper.Write(orders); } SelectMany - Compound from 3 public void Linq16() { List customers = GetCustomerList(); var orders = from c in customers, o in c.Orders where o.OrderDate >= new DateTime(1998, 1, 1) select new {c.CustomerID, o.OrderID, o.OrderDate}; ObjectDumper.Write(orders); } SelectMany - from Assignment public void Linq17() { List customers = GetCustomerList(); var orders = from c in customers, o in c.Orders, total = o.Total where total >= 2000.0M select new {c.CustomerID, o.OrderID, total}; ObjectDumper.Write(orders); } SelectMany - Multiple from public void Linq18() { List customers = GetCustomerList(); DateTime cutoffDate = new DateTime(1997, 1, 1); var orders = from c in customers where c.Region == "WA" from o in c.Orders where o.OrderDate >= cutoffDate select new {c.CustomerID, o.OrderID}; ObjectDumper.Write(orders); } SelectMany - Indexed public void Linq19() { List customers = GetCustomerList(); var customerOrders = customers.SelectMany( (cust, custIndex) => cust.Orders.Select(o => "Customer #" + (custIndex + 1) + " has an order with OrderID " + o.OrderID) ); ObjectDumper.Write(customerOrders); } Partitioning Operators Take - Simple public void Linq20() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var first3Numbers = numbers.Take(3); Console.WriteLine("First 3 numbers:"); foreach (var n in first3Numbers) { Console.WriteLine(n); } } Take - Nested public void Linq21() { List<Customer> customers = GetCustomerList(); var first3WAOrders = ( from c in customers from o in c.Orders where c.Region == "WA" select new {c.CustomerID, o.OrderID, o.OrderDate} ) .Take(3); Console.WriteLine("First 3 orders in WA:"); foreach (var order in first3WAOrders) { ObjectDumper.Write(order); } } Skip - Simple public void Linq22() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var allButFirst4Numbers = numbers.Skip(4); Console.WriteLine("All but first 4 numbers:"); foreach (var n in allButFirst4Numbers) { Console.WriteLine(n); } } Skip - Nested public void Linq23() { List<Customer> customers = GetCustomerList(); var waOrders = from c in customers from o in c.Orders where c.Region == "WA" select new {c.CustomerID, o.OrderID, o.OrderDate}; var allButFirst2Orders = waOrders.Skip(2); Console.WriteLine("All but first 2 orders in WA:"); foreach (var order in allButFirst2Orders) { ObjectDumper.Write(order); } } TakeWhile - Simple public void Linq24() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var firstNumbersLessThan6 = numbers.TakeWhile(n => n < 6); Console.WriteLine("First numbers less than 6:"); foreach (var n in firstNumbersLessThan6) { Console.WriteLine(n); } } SkipWhile - Simple public void Linq26() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var allButFirst3Numbers = numbers.SkipWhile(n => n % 3 != 0); Console.WriteLine("All elements starting from first element divisible by 3:"); foreach (var n in allButFirst3Numbers) { Console.WriteLine(n); } } SkipWhile - Indexed public void Linq27() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var laterNumbers = numbers.SkipWhile((n, index) => n >= index); Console.WriteLine("All elements starting from first element less than its position:"); foreach (var n in laterNumbers) { Console.WriteLine(n); } } Ordering Operators OrderBy - Simple 1 publicvoid Linq28() { string[] words = { "cherry", "apple", "blueberry" }; var sortedWords = from w in words orderby w select w; Console.WriteLine("The sorted list of words:"); foreach (var w in sortedWords) { Console.WriteLine(w); } } OrderBy - Simple 2 public void Linq29() { string[] words = { "cherry", "apple", "blueberry" }; var sortedWords = from w in words orderby w.Length select w; Console.WriteLine("The sorted list of words (by length):"); foreach (var w in sortedWords) { Console.WriteLine(w); } } OrderBy - Simple 3 public void Linq30() { List products = GetProductList(); var sortedProducts = from p in products orderby p.ProductName select p; ObjectDumper.Write(sortedProducts); } OrderBy - Comparer public class CaseInsensitiveComparer : IComparer<string> { public int Compare(string x, string y) { return string.Compare(x, y, true); } } public void Linq31() { string[] words = { "aPPLE", "AbAcUs", "bRaNcH", "BlUeBeRrY", "ClOvEr", "cHeRry"}; var sortedWords = words.OrderBy(a => a, new CaseInsensitiveComparer()); ObjectDumper.Write(sortedWords); } OrderByDescending - Simple 1 public void Linq32() { double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 }; var sortedDoubles = from d in doubles orderby d descending select d; Console.WriteLine("The doubles from highest to lowest:"); foreach (var d in sortedDoubles) { Console.WriteLine(d); } } OrderByDescending - Simple 2 public void Linq33() { List products = GetProductList(); var sortedProducts = from p in products orderby p.UnitsInStock descending select p; ObjectDumper.Write(sortedProducts); } OrderByDescending - Comparer public class CaseInsensitiveComparer : IComparerspan class="qs-keyword">string> { publicint Compare(string x, string y) { returnstring.Compare(x, y, true); } } publicvoid Linq34() { string[] words = { "aPPLE", "AbAcUs", "bRaNcH", "BlUeBeRrY", "ClOvEr", "cHeRry"}; var sortedWords = words.OrderByDescending(a => a, new CaseInsensitiveComparer()); ObjectDumper.Write(sortedWords); } ThenBy - Simple publicvoid Linq35() { string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; var sortedDigits = from d in digits orderby d.Length, d select d; Console.WriteLine("Sorted digits:"); foreach (var d in sortedDigits) { Console.WriteLine(d); } } ThenBy - Comparer public class CaseInsensitiveComparer : IComparerspan class="qs-keyword">string> { publicint Compare(string x, string y) { returnstring.Compare(x, y, true); } } publicvoid Linq36() { string[] words = { "aPPLE", "AbAcUs", "bRaNcH", "BlUeBeRrY", "ClOvEr", "cHeRry"}; var sortedWords = words.OrderBy(a => a.Length) .ThenBy(a => a, new CaseInsensitiveComparer()); ObjectDumper.Write(sortedWords); } ThenByDescending - Simple publicvoid Linq37() { List products = GetProductList();var sortedProducts = from p in products orderby p.Category, p.UnitPrice descendingselect p; ObjectDumper.Write(sortedProducts); } ThenByDescending - Comparer public class CaseInsensitiveComparer : IComparerspan class="qs-keyword">string> { publicint Compare(string x, string y) { returnstring.Compare(x, y, true); } } publicvoid Linq38() { string[] words = { "aPPLE", "AbAcUs", "bRaNcH", "BlUeBeRrY", "ClOvEr", "cHeRry"}; var sortedWords = words.OrderBy(a => a.Length) .ThenByDescending(a => a, new CaseInsensitiveComparer()); ObjectDumper.Write(sortedWords); } Reverse publicvoid Linq39() { string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; var reversedIDigits = ( from d in digits where d[1] == 'i' select d) .Reverse(); Console.WriteLine("A backwards list of the digits with a second character of 'i':"); foreach (var d in reversedIDigits) { Console.WriteLine(d); } } Grouping Operators GroupBy - Simple 1 public void Linq40() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var numberGroups = from n in numbers group n by n % 5 into g select new { Remainder = g.Key, Numbers = g }; foreach (var g in numberGroups) { Console.WriteLine("Numbers with a remainder of {0} when divided by 5:", g.Remainder); foreach (var n in g.Numbers) { Console.WriteLine(n); } } } GroupBy - Simple 2 public void Linq41() { string[] words = { "blueberry", "chimpanzee", "abacus", "banana", "apple", "cheese" }; var wordGroups = from w in words group w by w[0] into g select new { FirstLetter = g.Key, Words = g }; foreach (var g in wordGroups) { Console.WriteLine("Words that start with the letter '{0}':", g.FirstLetter); foreach (var w in g.Words) { Console.WriteLine(w); } } } GroupBy - Simple 3 public void Linq42() { List<Product> products = GetProductList(); var orderGroups = from p in products group p by p.Category into g select new { Category = g.Key, Products = g }; ObjectDumper.Write(orderGroups, 1); } GroupBy - Nested public void Linq43() { List<Customer> customers = GetCustomerList(); var customerOrderGroups = from c in customers select new {c.CompanyName, YearGroups = from o in c.Orders group o by o.OrderDate.Year into yg select new {Year = yg.Key, MonthGroups = from o in yg group o by o.OrderDate.Month into mg select new { Month = mg.Key, Orders = mg } } }; ObjectDumper.Write(customerOrderGroups, 3); } GroupBy - Comparer public class AnagramEqualityComparer : IEqualityComparer { public bool Equals(string x, string y) { return getCanonicalString(x) == getCanonicalString(y); } public int GetHashCode(string obj) { return getCanonicalString(obj).GetHashCode(); } private string getCanonicalString(string word) { char[] wordChars = word.ToCharArray(); Array.Sort(wordChars); return new string(wordChars); } } publicvoid Linq44() { string[] anagrams = {"from ", " salt", " earn ", " last ", " near ", " form "}; var orderGroups = anagrams.GroupBy(w => w.Trim(), new AnagramEqualityComparer()); ObjectDumper.Write(orderGroups, 1); } GroupBy - Comparer, Mapped public void Linq45() { string[] anagrams = {"from ", " salt", " earn ", " last ", " near ", " form "}; var orderGroups = anagrams.GroupBy( w => w.Trim(), a => a.ToUpper(), new AnagramEqualityComparer() ); ObjectDumper.Write(orderGroups, 1); } public class AnagramEqualityComparer : IEqualityComparer<string> { public bool Equals(string x, string y) { return getCanonicalString(x) == getCanonicalString(y); } public int GetHashCode(string obj) { return getCanonicalString(obj).GetHashCode(); } private string getCanonicalString(string word) { char[] wordChars = word.ToCharArray(); Array.Sort<char>(wordChars); return new string(wordChars); } } Set Operators Distinct - 1 publicvoid Linq46() { int[] factorsOf300 = { 2, 2, 3, 5, 5 }; var uniqueFactors = factorsOf300.Distinct(); Console.WriteLine("Prime factors of 300:"); foreach (var f in uniqueFactors) { Console.WriteLine(f); } } Distinct - 2 public void Linq47() { List products = GetProductList(); var categoryNames = ( from p in products select p.Category) .Distinct(); Console.WriteLine("Category names:"); foreach (var n in categoryNames) { Console.WriteLine(n); } } Union - 1 publicvoid Linq48() { int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; int[] numbersB = { 1, 3, 5, 7, 8 }; var uniqueNumbers = numbersA.Union(numbersB); Console.WriteLine("Unique numbers from both arrays:"); foreach (var n in uniqueNumbers) { Console.WriteLine(n); } } Union - 2 publicvoid Linq49() { List products = GetProductList();List customers = GetCustomerList(); var productFirstChars = from p in products select p.ProductName[0]; var customerFirstChars = from c in customers select c.CompanyName[0]; var uniqueFirstChars = productFirstChars.Union(customerFirstChars); Console.WriteLine("Unique first letters from Product names and Customer names:"); foreach (var ch in uniqueFirstChars) { Console.WriteLine(ch); } } Intersect - 1 publicvoid Linq50() { int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; int[] numbersB = { 1, 3, 5, 7, 8 }; var commonNumbers = numbersA.Intersect(numbersB); Console.WriteLine("Common numbers shared by both arrays:"); foreach (var n in commonNumbers) { Console.WriteLine(n); } } Intersect - 2 publicvoid Linq51() { List products = GetProductList(); List customers = GetCustomerList(); var productFirstChars = from p in products select p.ProductName[0]; var customerFirstChars = from c in customers select c.CompanyName[0]; var commonFirstChars = productFirstChars.Intersect(customerFirstChars); Console.WriteLine("Common first letters from Product names and Customer names:"); foreach (var ch in commonFirstChars) { Console.WriteLine(ch); } } Except - 1 public void Linq52() { int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; int[] numbersB = { 1, 3, 5, 7, 8 }; IEnumerable<int> aOnlyNumbers = numbersA.Except(numbersB); Console.WriteLine("Numbers in first array but not second array:"); foreach (var n in aOnlyNumbers) { Console.WriteLine(n); } } Except - 2 public void Linq53() { List products = GetProductList(); List customers = GetCustomerList(); var productFirstChars = from p in products select p.ProductName[0]; var customerFirstChars = from c in customers select c.CompanyName[0]; var productOnlyFirstChars = productFirstChars.Except(customerFirstChars); Console.WriteLine("First letters from Product names, but not from Customer names:"); foreach (var ch in productOnlyFirstChars) { Console.WriteLine(ch); } } Conversion Operators To Array public void Linq54() { double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 }; var sortedDoubles = from d in doubles orderby d descending select d; var doublesArray = sortedDoubles.ToArray(); Console.WriteLine("Every other double from highest to lowest:"); for (int d = 0; d < doublesArray.Length; d += 2) { Console.WriteLine(doublesArray[d]); } } To List public void Linq55() { string[] words = { "cherry", "apple", "blueberry" }; var sortedWords = from w in words orderby w select w; var wordList = sortedWords.ToList(); Console.WriteLine("The sorted word list:"); foreach (var w in wordList) { Console.WriteLine(w); } } To Dictionary public void Linq56() { 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"]); } OfType public void Linq57() { object[] numbers = { null, 1.0, "two", 3, 4.0f, 5, "six", 7.0 }; var doubles = numbers.OfType<double>(); Console.WriteLine("Numbers stored as doubles:"); foreach (var d in doubles) { Console.WriteLine(d); } } Element Operators First - Simple public void Linq58() { List products = GetProductList(); Product product12 = ( from p in products where p.ProductID == 12 select p ) .First(); ObjectDumper.Write(product12); } First - Indexed public void Linq60() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int evenNum = numbers.First((num, index) => (num % 2 == 0) && (index % 2 == 0)); Console.WriteLine("{0} is an even number at an even position within the list.", evenNum); } FirstOrDefault - Simple public void Linq61() { int[] numbers = {}; int firstNumOrDefault = numbers.FirstOrDefault(); Console.WriteLine(firstNumOrDefault); } FirstOrDefault - Condition public void Linq62() { List products = GetProductList(); Product product789 = products.FirstOrDefault(p => p.ProductID == 789); Console.WriteLine("Product 789 exists: {0}", product789 != null); } FirstOrDefault - Indexed public void Linq63() { double?[] doubles = { 1.7, 2.3, 4.1, 1.9, 2.9 }; double? num = doubles.FirstOrDefault((n, index) => (n >= index - 0.5 && n <= index + 0.5)); if (num != null) Console.WriteLine("The value {1} is within 0.5 of its index position.", num); else Console.WriteLine("There is no number within 0.5 of its index position.", num); } ElementAt public void Linq64() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int fourthLowNum = ( from n in numbers where n < 5 select n ) .ElementAt(3); // 3 because sequences use 0-based indexing Console.WriteLine("Fourth number < 5: {0}", fourthLowNum); } Generation Operators Range public void Linq65() { var numbers = from n in Sequence.Range(100, 50) selectnew {Number = n, OddEven = n % 2 == 1 ? "odd" : "even"}; foreach (var n in numbers) { Console.WriteLine("The number {0} is {1}.", n.Number, n.OddEven); } } Repeat public void Linq66() { var numbers = Sequence.Repeat(7, 10); foreach (var n in numbers) { Console.WriteLine(n); } } Quantifiers Any - Simple public void Linq67() { string[] words = { "believe", "relief", "receipt", "field" }; bool iAfterE = words.Any(w => w.Contains("ei")); Console.WriteLine("There is a word that contains in the list that contains 'ei': {0}", iAfterE); } Any - Indexed public void Linq68() { int[] numbers = { -9, -4, -8, -3, -5, -2, -1, -6, -7 }; bool negativeMatch = numbers.Any((n, index) => n == -index); Console.WriteLine("There is a number that is the negative of its index: {0}", negativeMatch); } Any - Grouped public void Linq69() { List products = GetProductList(); var productGroups = from p in products group p by p.Category into g where g.Group.Any(p => p.UnitsInStock == 0) select new {Category = g.Key, Products = g.Group}; ObjectDumper.Write(productGroups, 1); } All - Simple public void Linq70() { int[] numbers = { 1, 11, 3, 19, 41, 65, 19 }; bool onlyOdd = numbers.All(n => n % 2 == 1); Console.WriteLine("The list contains only odd numbers: {0}", onlyOdd); } All - Indexed public void Linq71() { int[] lowNumbers = { 1, 11, 3, 19, 41, 65, 19 }; int[] highNumbers = { 7, 19, 42, 22, 45, 79, 24 }; bool allLower = lowNumbers.All((num, index) => num < highNumbers[index]); Console.WriteLine("Each number in the first list is lower than its counterpart in the second list: {0}", allLower); } All - Grouped public void Linq72() { List products = GetProductList(); var productGroups = from p in products group p by p.Category into g where g.Group.All(p => p.UnitsInStock > 0) select new {Category = g.Key, Products = g.Group}; ObjectDumper.Write(productGroups, 1); } Aggregate Operators Count - Simple public void Linq73() { int[] factorsOf300 = { 2, 2, 3, 5, 5 }; int uniqueFactors = factorsOf300.Distinct().Count(); Console.WriteLine("There are {0} unique factors of 300.", uniqueFactors); } Count - Conditional public void Linq74() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int oddNumbers = numbers.Count(n => n % 2 == 1); Console.WriteLine("There are {0} odd numbers in the list.", oddNumbers); } Count - Indexed public void Linq75() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int oddEvenMatches = numbers.Count((n, index) => n % 2 == index % 2); Console.WriteLine("There are {0} numbers in the list whose odd/even status " + "matches that of their position.", oddEvenMatches); } Count - Nested public void Linq76() { List customers = GetCustomerList(); var orderCounts = from c in customers select new {c.CustomerID, OrderCount = c.Orders.Count()}; ObjectDumper.Write(orderCounts); } Count - Grouped public void Linq77() { List products = GetProductList(); var categoryCounts = from p in products group p by p.Category into g select new {Category = g.Key, ProductCount = g.Group.Count()}; ObjectDumper.Write(categoryCounts); } Sum - Simple public void Linq78() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; double numSum = numbers.Sum(); Console.WriteLine("The sum of the numbers is {0}.", numSum); } Sum - Projection public void Linq79() { string[] words = { "cherry", "apple", "blueberry" }; double totalChars = words.Sum(w => w.Length); Console.WriteLine("There are a total of {0} characters in these words.", totalChars); } Sum - Grouped public void Linq80() { List products = GetProductList(); var categories = from p in products group p by p.Category into g select new {Category = g.Key, TotalUnitsInStock = g.Group.Sum(p => p.UnitsInStock)}; ObjectDumper.Write(categories); } Min - Simple public void Linq81() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int minNum = numbers.Min(); Console.WriteLine("The minimum number is {0}.", minNum); } Min - Projection public void Linq82() { string[] words = { "cherry", "apple", "blueberry" }; int shortestWord = words.Min(w => w.Length); Console.WriteLine("The shortest word is {0} characters long.", shortestWord); } Min - Grouped public void Linq83() { List products = GetProductList(); var categories = from p in products group p by p.Category into g select new {Category = g.Key, CheapestPrice = g.Group.Min(p => p.UnitPrice)}; ObjectDumper.Write(categories); } Min - Elements public void Linq84() { List products = GetProductList(); var categories = from p in products group p by p.Category into g from minPrice = g.Group.Min(p => p.UnitPrice) select new {Category = g.Key, CheapestProducts = g.Group.Where(p => p.UnitPrice == minPrice)}; ObjectDumper.Write(categories, 1); } Max - Simple public void Linq85() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int maxNum = numbers.Max(); Console.WriteLine("The maximum number is {0}.", maxNum); } Max - Projection public void Linq86() { string[] words = { "cherry", "apple", "blueberry" }; int longestLength = words.Max(w => w.Length); Console.WriteLine("The longest word is {0} characters long.", longestLength); } Max - Grouped public void Linq87() { List products = GetProductList(); var categories = from p in products group p by p.Category into g select new {Category = g.Key, MostExpensivePrice = g.Group.Max(p => p.UnitPrice)}; ObjectDumper.Write(categories); } Max - Elements public void Linq88() { List products = GetProductList(); var categories = from p in products group p by p.Category into g from maxPrice = g.Group.Max(p => p.UnitPrice) select new {Category = g.Key, MostExpensiveProducts = g.Group.Where(p => p.UnitPrice == maxPrice)}; ObjectDumper.Write(categories, 1); } Average - Simple public void Linq89() { int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; double averageNum = numbers.Average(); Console.WriteLine("The average number is {0}.", averageNum); } Average - Projection public void Linq90() { string[] words = { "cherry", "apple", "blueberry" }; double averageLength = words.Average(w => w.Length); Console.WriteLine("The average word length is {0} characters.", averageLength); } Average - Grouped public void Linq91() { List products = GetProductList(); var categories = from p in products group p by p.Category into g select new {Category = g.Key, AveragePrice = g.Group.Average(p => p.UnitPrice)}; ObjectDumper.Write(categories); } Fold - Simple public void Linq92() { double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 }; double product = doubles.Fold((runningProduct, nextFactor) => runningProduct * nextFactor); Console.WriteLine("Total product of all numbers: {0}", product); } Fold - Seed public void Linq93() { double startBalance = 100.0; int[] attemptedWithdrawals = { 20, 10, 40, 50, 10, 70, 30 }; double endBalance = attemptedWithdrawals.Fold(startBalance, (balance, nextWithdrawal) => ( (nextWithdrawal <= balance) ? (balance - nextWithdrawal) : balance ) ); Console.WriteLine("Ending balance: {0}", endBalance); } Miscellaneous Operators Concat - 1 public void Linq94() { int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; int[] numbersB = { 1, 3, 5, 7, 8 }; var allNumbers = numbersA.Concat(numbersB); Console.WriteLine("All numbers from both arrays:"); foreach (var n in allNumbers) { Console.WriteLine(n); } } Concat - 2 public void Linq95() { List customers = GetCustomerList(); List products = GetProductList(); var customerNames = from c in customers select c.CompanyName; var productNames = from p in products select p.ProductName; var allNames = customerNames.Concat(productNames); Console.WriteLine("Customer and product names:"); foreach (var n in allNames) { Console.WriteLine(n); } } EqualAll - 1 public void Linq96() { var wordsA = new string[] { "cherry", "apple", "blueberry" }; var wordsB = new string[] { "cherry", "apple", "blueberry" }; bool match = wordsA.EqualAll(wordsB); Console.WriteLine("The sequences match: {0}", match); } EqualAll - 2 public void Linq97() { var wordsA = new string[] { "cherry", "apple", "blueberry" }; var wordsB = new string[] { "apple", "blueberry", "cherry" }; bool match = wordsA.EqualAll(wordsB); Console.WriteLine("The sequences match: {0}", match); } Custom Sequence Operators Combine public static class CustomSequenceOperators { public static IEnumerable Combine(this IEnumerable first, IEnumerable second, Func func) { using (IEnumerator e1 = first.GetEnumerator(), e2 = second.GetEnumerator()) { while (e1.MoveNext() && e2.MoveNext()) { yield return func(e1.Current, e2.Current); } } } } public void Linq98() { int[] vectorA = { 0, 2, 4, 5, 6 }; int[] vectorB = { 1, 3, 5, 7, 8 }; int dotProduct = vectorA.Combine(vectorB, (a, b) => a * b).Sum(); Console.WriteLine("Dot product: {0}", dotProduct); } Query Execution Deferred public void Linq99() { // Sequence operators form first-class queries that // are not executed until you enumerate over them. int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int i = 0; var q = from n in numbers select ++i; // Note, the local variable 'i' is not incremented // until each element is evaluated (as a side-effect): foreach (var v in q) { Console.WriteLine("v = {0}, i = {1}", v, i); } } Immediate public void Linq100() { // Methods like ToList() cause the query to be // executed immediately, caching the results. int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int i = 0; var q = ( from n in numbers select ++i ) .ToList(); // The local variable i has already been fully // incremented before we iterate the results: foreach (var v in q) { Console.WriteLine("v = {0}, i = {1}", v, i); } } Query Reuse public void Linq101() { // Deferred execution lets us define a query once // and then reuse it later after data changes. int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var lowNumbers = from n in numbers where n <= 3 select n; Console.WriteLine("First run numbers <= 3:"); foreach (int n in lowNumbers) { Console.WriteLine(n); } for (int i = 0; i < 10; i++) { numbers[i] = -numbers[i]; } // During this second run, the same query object, // lowNumbers, will be iterating over the new state // of numbers[], producing different results: Console.WriteLine("Second run numbers <= 3:"); foreach (int n in lowNumbers) { Console.WriteLine(n); } } 阅读全文
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