LINQ

Use index when querying array with LINQ

Posted on by coder 
   
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Drawing;

public class Book {
    public String Title { get; set; }

    public override String ToString() {
        return Title;
    }
}

class Program {


    static public Book[] Books =
    {
      new Book {Title="F"},
      new Book {Title="B"}
    };

    static void Main(string[] args) {
        var books =
          Books
            .Select((book, index) => new { index, book.Title })
            .OrderBy(book => book.Title);
    }
}

Select – Indexed: prints the value of the integer and whether it matches its index in the array

Posted on by coder 
   
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
    public static void Main() {

        int[] numbers = { 5, 4, 1, 3, 9};

        var numsInPlace = numbers.Select((num, index) => new { Num = num, InPlace = (num == index) });

        foreach (var n in numsInPlace) {
            Console.WriteLine("{0}: {1}", n.Num, n.InPlace);
        }
    }
}

Use an indexed Where clause (where the length of the number's name is shorter than its value)

Posted on by coder

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
public static void Main() {

string[] digits = { “zero”, “one”, “two”, “three”, “four”, “five”, “six”, “seven”, “eight”, “nine” };

var shortDigits = digits.Where((digit, index) => digit.Length < index); foreach (var d in shortDigits) { Console.WriteLine("The word {0} is shorter than its value.", d); } } } [/csharp]

Query by position

Posted on by coder 
   
 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using System.Reflection;

class Person {
    int _id;
    int _idRole;
    string _lastName;
    string _firstName;

    public int ID {
        get { return _id; }
        set { _id = value; }
    }

    public int IDRole {
        get { return _idRole; }
        set { _idRole = value; }
    }

    public string LastName {
        get { return _lastName; }
        set { _lastName = value; }
    }

    public string FirstName {
        get { return _firstName; }
        set { _firstName = value; }
    }
}
class Program {
    static void Main(string[] args) {
        List<Person> people = new List<Person> {
               new Person { ID = 1, IDRole = 1, LastName = "A", FirstName = "B"},
               new Person { ID = 2, IDRole = 2, LastName = "G", FirstName = "T"},
               new Person { ID = 3, IDRole = 2, LastName = "G", FirstName = "M"},
               new Person { ID = 4, IDRole = 3, LastName = "C", FirstName = "G"}
            };
        var query = people.Select((p, index) => new { Position = index, p.FirstName, p.LastName });
    }
}

GroupJoin Operator

Posted on by coder 
   
 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

public class Employee {
    public int id;
    public string firstName;
    public string lastName;

    public static ArrayList GetEmployeesArrayList() {
        ArrayList al = new ArrayList();
        al.Add(new Employee { id = 1, firstName = "J", lastName = "R" });
        al.Add(new Employee { id = 2, firstName = "W", lastName = "G" });
        al.Add(new Employee { id = 3, firstName = "A", lastName = "H" });
        al.Add(new Employee { id = 4, firstName = "D", lastName = "L" });
        al.Add(new Employee { id = 101, firstName = "K", lastName = "F" });
        return (al);
    }

    public static Employee[] GetEmployeesArray() {
        return ((Employee[])GetEmployeesArrayList().ToArray());
    }
}
public class EmployeeOptionEntry {
    public int id;
    public long optionsCount;
    public DateTime dateAwarded;

    public static EmployeeOptionEntry[] GetEmployeeOptionEntries() {
        EmployeeOptionEntry[] empOptions = new EmployeeOptionEntry[] {
      new EmployeeOptionEntry {
        id = 1,
        optionsCount = 2,
         dateAwarded = DateTime.Parse("1999/12/31") },
       new EmployeeOptionEntry {
        id = 101,
        optionsCount = 2,
        dateAwarded = DateTime.Parse("1998/12/31") }
    };

        return (empOptions);
    }
}
public class MainClass {
    public static void Main() {
        Employee[] employees = Employee.GetEmployeesArray();
        EmployeeOptionEntry[] empOptions = EmployeeOptionEntry.GetEmployeeOptionEntries();

        var employeeOptions = employees
          .GroupJoin(
            empOptions,
             e => e.id,
             o => o.id,
             (e, os) => new {
                 id = e.id,
                 name = string.Format("{0} {1}", e.firstName, e.lastName),
                 options = os.Sum(o => o.optionsCount)
             });

        foreach (var item in employeeOptions)
            Console.WriteLine(item);
    }
}

uses GroupBy to partition trimmed elements of an array using a custom comparer

Posted on by coder 
   
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
    public static void Main() {

        string[] anagrams = { "from ", " salt", " earn ", " last ", " near ", " form " };

        var orderGroups = anagrams.GroupBy(
                    w => w.Trim(),
                    a => a.ToUpper(),
                    new AnagramEqualityComparer()
                    );

        foreach (var v in orderGroups) {
            Console.WriteLine(v);
        }
    }

    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);
        }
    }
}

uses group by to partition a list of each customer's orders, first by year, and then by month.

Posted on by coder

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
public static void Main() {

List 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 }
}
};

Console.Write(customerOrderGroups);
}
static List GetCustomerList() {
List empTree = new List();
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 });

List l = new List();
l.Add(new Customer { CompanyName = “A”, Region = “R1”, UnitsInStock = 1, Orders = empTree, CustomerId = 0 });
l.Add(new Customer { CompanyName = “B”, Region = “R2”, UnitsInStock = 2, Orders = empTree, CustomerId = 1 });
l.Add(new Customer { CompanyName = “C”, Region = “R3”, UnitsInStock = 3, Orders = empTree, CustomerId = 2 });
l.Add(new Customer { CompanyName = “D”, Region = “R4”, UnitsInStock = 4, Orders = empTree, CustomerId = 3 });
l.Add(new Customer { CompanyName = “E”, Region = “R5”, UnitsInStock = 5, Orders = empTree, CustomerId = 4 });
return l;
}
}
class Customer : IComparable {
public string CompanyName { get; set; }
public string Region { get; set; }
public List Orders { get; set; }
public int UnitsInStock { get; set; }
public int CustomerId { get; set; }

public override string ToString() {
return String.Format(“Id: {0}, Name: {1}, Region: {3}”, this.CustomerId, this.CompanyName, this.Region);
}
int IComparable.CompareTo(Customer other) {
if (other == null)
return 1;

if (this.CustomerId > other.CustomerId)
return 1;

if (this.CustomerId < other.CustomerId) return -1; return 0; } } class Product : IComparable {
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.CompareTo(Product other) {
if (other == null)
return 1;
if (this.Id > other.Id)
return 1;

if (this.Id < other.Id) return -1; return 0; } } [/csharp]