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Where

Input:	IEnumerable<TSource>
Lambda expression:	TSource => bool or (TSource,int) => bool
Query syntax:	where boolExpression

Where returns the elements that satisfy the given expression.

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

class Program
{
    static void Main()
    {
        string[] names = { "Java", "C#", "Javascript", "SQL", "Oracle", "Python", "C++", "C", "HTML", "CSS" };

        IEnumerable<string> query = names.Where(name => name.EndsWith("e"));

        foreach (string s in query)
        {
            Console.WriteLine(s);
        }

    }
}

The output:


Oracle

In query syntax:

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

class Program
{
    static void Main()
    {
        string[] names = { "Java", "C#", "Javascript", "SQL", "Oracle", "Python", "C++", "C", "HTML", "CSS" };


        IEnumerable<string> query = from n in names where n.EndsWith("e") select n;

        foreach (string s in query)
        {
            Console.WriteLine(s);
        }
    }
}

The output:


Oracle

A where clause can appear more than once in a query:

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

class Program
{
    static void Main()
    {
        string[] names = { "Java", "C#", "Javascript", "SQL", "Oracle", "Python", "C++", "C", "HTML", "CSS" };

        IEnumerable<string> query =
                                    from n in names
                                    where n.Length > 3
                                    let u = n.ToUpper()
                                    where u.EndsWith("E")
                                    select u;

        foreach (string s in query)
        {
            Console.WriteLine(s);
        }
    }
}

The output:


ORACLE

Indexed filtering where expression

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

class Program
{
    static void Main()
    {
        string[] names = { "Java", "C#", "Javascript", "SQL", "Oracle", "Python", "C++", "C", "HTML", "CSS" };

        IEnumerable<string> query = names.Where((n, i) => i % 2 == 0);

        foreach (string s in query)
        {
            Console.WriteLine(s);
        }
    }
}

The output:


Java
Javascript
Oracle
C++
HTML

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