Csharp/C Sharp/LINQ/select
Содержание
- 1 Converting an Array of Strings to Integers
- 2 Converting an Array of Strings to Integers and Sorting It
- 3 Demonstrating the Query Results Changing Between Enumerations
- 4 Query Reuse
- 5 Query with Intentional Exception Deferred Until Enumeration
- 6 Returning a List
- 7 Select array item by type
- 8 Select with Anonymous Types: iterates over each element to print the element"s name
- 9 Select with Anonymous Types: prints the name of every product in the product list along with the category of the product and its unit price
- 10 Select with Anonymous Types: prints uppercase and lowercase versions of each string in an input array
- 11 Transformation: link two array.
- 12 Use LINQ to query characters in a string
- 13 Use LINQ with Dictionary
- 14 uses select to create a sequence of each product name.
Converting an Array of Strings to Integers
<source lang="csharp"> using System; using System.Linq; public class MainClass {
public static void Main() {
string[] numbers = { "0042", "010", "9", "2q7" };
int[] nums = numbers.Select(s => Int32.Parse(s)).ToArray();
}
}
</source>
Converting an Array of Strings to Integers and Sorting It
<source lang="csharp"> using System; using System.Linq; public class MainClass {
public static void Main() {
string[] numbers = { "0042", "010", "9", "2q7" };
int[] nums = numbers.Select(s => Int32.Parse(s)).OrderBy(s => s).ToArray();
foreach (int num in nums)
Console.WriteLine(num);
}
}
</source>
Demonstrating the Query Results Changing Between Enumerations
<source lang="csharp"> using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass {
public static void Main() {
int[] intArray = new int[] { 1, 2, 3 };
IEnumerable<int> ints = intArray.Select(i => i);
foreach (int i in ints)
Console.WriteLine(i);
intArray[0] = 5;
foreach (int i in ints)
Console.WriteLine(i);
}
}
</source>
Query Reuse
<source lang="csharp"> using System; using System.Linq; static class QueryReuse {
static double Square(double n) {
Console.WriteLine("Computing Square(" + n + ")...");
return Math.Pow(n, 2);
}
public static void Main() {
int[] numbers = { 1, 2, 3 };
var query =
from n in numbers
select Square(n);
foreach (var n in query)
Console.WriteLine(n);
for (int i = 0; i < numbers.Length; i++)
numbers[i] = numbers[i] + 10;
foreach (var n in query)
Console.WriteLine(n);
}
}
</source>
Query with Intentional Exception Deferred Until Enumeration
<source lang="csharp"> using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass {
public static void Main() {
string[] strings = { "one", "two", null, "three" };
Console.WriteLine("Before Where() is called.");
IEnumerable<string> ieStrings = strings.Where(s => s.Length == 3);
Console.WriteLine("After Where() is called.");
foreach (string s in ieStrings) {
Console.WriteLine("Processing " + s);
}
}
}
</source>
Returning a List
<source lang="csharp"> using System; using System.Linq; using System.Collections; using System.Collections.Generic; public class MainClass {
public static void Main() {
int[] intArray = new int[] { 1, 2, 3 };
List<int> ints = intArray.Select(i => i).ToList();
foreach (int i in ints)
Console.WriteLine(i);
intArray[0] = 5;
foreach (int i in ints)
Console.WriteLine(i);
}
}
</source>
Select array item by type
<source lang="csharp"> using System; using System.Linq; static class TestArray {
static void Main() {
Object[] array = { "String", 12, true, "a" };
var types =
array
.Select(item => item.GetType().Name)
.OrderBy(type => type);
}
}
</source>
Select with Anonymous Types: iterates over each element to print the element"s name
<source lang="csharp"> using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {
public static void Main() {
int[] numbers = { 5, 4, 1};
string[] strings = { "zero", "one", "two"};
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");
}
}
}
</source>
Select with Anonymous Types: prints the name of every product in the product list along with the category of the product and its unit price
<source lang="csharp"> using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {
public static void Main() {
List<Product> 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);
}
}
static List<Product> GetProductList() {
List<Product> empTree = new List<Product>();
empTree.Add(new Product { ProductName = "A", Category = "O", UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "B", Category = "O", UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "C", Category = "O", UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "D", Category = "O", UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "E", Category = "O", UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "F", Category = "O", UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
return empTree;
}
} class Product : IComparable<Product> {
public string ProductName { get; set; }
public string Category { get; set; }
public int UnitPrice { get; set; }
public int UnitsInStock { get; set; }
public int Total { get; set; }
public DateTime OrderDate { get; set; }
public int Id { get; set; }
public override string ToString() {
return String.Format("Id: {0}, Name: {1} , Category: {3}", this.Id, this.ProductName, this.Category);
}
int IComparable<Product>.rupareTo(Product other) {
if (other == null)
return 1;
if (this.Id > other.Id)
return 1;
if (this.Id < other.Id)
return -1;
return 0;
}
}
</source>
Select with Anonymous Types: prints uppercase and lowercase versions of each string in an input array
<source lang="csharp"> using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {
public static void Main() {
string[] words = { "Abc", "aBc", "AAA" };
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);
}
}
}
</source>
Transformation: link two array.
<source lang="csharp"> using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {
public static void Main() {
int[] numbers = { 5, 4, 1};
string[] strings = { "zero", "one", "two"};
var textNums =
from n in numbers
select strings[n];
Console.WriteLine("Number strings:");
foreach (var s in textNums) {
Console.WriteLine(s);
}
}
}
</source>
Use LINQ to query characters in a string
<source lang="csharp"> using System; using System.Collections.Generic; using System.Linq; static class TestString {
static void Main() {
var count =
"abc 8"
.Where(c => !Char.IsLetter(c))
.Count();
Console.WriteLine(count);
}
}
</source>
Use LINQ with Dictionary
<source lang="csharp"> using System; using System.Collections.Generic; using System.Linq; static class TestDictionary {
static void Main() {
Dictionary<int, string> frenchNumbers;
frenchNumbers = new Dictionary<int, string>();
frenchNumbers.Add(0, "zero");
frenchNumbers.Add(1, "one");
frenchNumbers.Add(2, "two");
frenchNumbers.Add(3, "three");
frenchNumbers.Add(4, "four");
var evenFrenchNumbers =
from entry in frenchNumbers
where (entry.Key % 2) == 0
select entry.Value;
}
}
</source>
uses select to create a sequence of each product name.
<source lang="csharp"> using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass {
public static void Main() {
List<Product> products = GetProductList();
var productNames =
from p in products
select p.ProductName;
foreach (var productName in productNames) {
Console.WriteLine(productName);
}
}
static List<Product> GetProductList() {
List<Product> empTree = new List<Product>();
empTree.Add(new Product { ProductName = "A", Category = "O", UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "B", Category = "O", UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "C", Category = "O", UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "D", Category = "O", UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "E", Category = "O", UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = "F", Category = "O", UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
return empTree;
}
} class Product : IComparable<Product> {
public string ProductName { get; set; }
public string Category { get; set; }
public int UnitPrice { get; set; }
public int UnitsInStock { get; set; }
public int Total { get; set; }
public DateTime OrderDate { get; set; }
public int Id { get; set; }
public override string ToString() {
return String.Format("Id: {0}, Name: {1} , Category: {3}", this.Id, this.ProductName, this.Category);
}
int IComparable<Product>.rupareTo(Product other) {
if (other == null)
return 1;
if (this.Id > other.Id)
return 1;
if (this.Id < other.Id)
return -1;
return 0;
}
}
</source>
