101个LINQ示例，包含几乎全部操作
2018-07-20 来源：open-open
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);
}
}
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