Csharp/CSharp Tutorial/LINQ/Filter

Calling the Common Library Filter Method

using System.Collections;
using System;
public delegate bool IntFilter(int i);
public class MainClass {
    public static void Main() {
        int[] nums = { 1, 2, 3, 4, 5, 6};
        int[] oddNums = FilterArrayOfInts(nums, IsOdd);
        foreach (int i in oddNums)
            Console.WriteLine(i);
    }
    public static bool IsOdd(int i) {
        return ((i & 1) == 1);
    }
    public static int[] FilterArrayOfInts(int[] ints, IntFilter filter) {
        ArrayList aList = new ArrayList();
        foreach (int i in ints) {
            if (filter(i)) {
                aList.Add(i);
            }
        }
        return ((int[])aList.ToArray(typeof(int)));
    }
}

Calling the Filter Method with a Lambda Expression

using System;
using System.Collections;
public delegate bool IntFilter(int i);
public class MainClass {
    public static int[] FilterArrayOfInts(int[] ints, IntFilter filter) {
        ArrayList aList = new ArrayList();
        foreach (int i in ints) {
            if (filter(i)) {
                aList.Add(i);
            }
        }
        return ((int[])aList.ToArray(typeof(int)));
    }
    public static void Main() {
        int[] nums = { 1, 2, 3, 4, 5};
        int[] oddNums = FilterArrayOfInts(nums, i => ((i & 1) == 1));
        foreach (int i in oddNums)
            Console.WriteLine(i);
    }
}

Calling the Filter Method with an Anonymous Method

using System;
using System.Collections;
public delegate bool IntFilter(int i);
public class MainClass {
    public static int[] FilterArrayOfInts(int[] ints, IntFilter filter) {
        ArrayList aList = new ArrayList();
        foreach (int i in ints) {
            if (filter(i)) {
                aList.Add(i);
            }
        }
        return ((int[])aList.ToArray(typeof(int)));
    }
    public static void Main() {
        int[] nums = { 1, 2, 3, 4, 5, 6};
        int[] oddNums = FilterArrayOfInts(nums, delegate(int i) { return ((i & 1) == 1); });
        foreach (int i in oddNums)
            Console.WriteLine(i);
    }
}

Use delegate to create a filter

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Reflection;
using System.Linq;
using System.Xml;
using System.Xml.Linq;
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"}
            };
        Func<Person, bool> filter = delegate(Person p) { return p.ID == 1; };
        var query = people
                    .Where(filter)
                    .Select(p => new { p.FirstName, p.LastName });
    }
}