C# - Enumerable.Select Method

public static System.Collections.Generic.IEnumerable<TResult> Select<TSource,TResult>

             (this System.Collections.Generic.IEnumerable<TSource> source,  

                                                            Func<TSource,int,TResult> selector);

Type Parameters

TSource

The type of the elements of source.

TResult

The type of the value returned by selector.

Parameters

source

IEnumerable<TSource>

A sequence of values to invoke a transform function on.

selector

Func<TSource,Int32,TResult>

A transform function to apply to each source element; the second parameter of the function represents the index of the source element.

Returns

IEnumerable<TResult>

An IEnumerable<T> whose elements are the result of invoking the transform function on each element of source.

Exceptions

ArgumentNullException

source or selector is null.

Example

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

namespace Test

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            string[] fruits = { "apple", "banana", "mango", 
                                "orange", "passionfruit", "grape" };

            var query =

                       fruits.Select((fruit, index) => 

                                new { index, str = fruit.Substring(0, index) });

            foreach (var obj in query)

            {

                Console.WriteLine("{0}", obj);

            }

            /*

             This code produces the following output:

             {index=0, str=}

             {index=1, str=b}

             {index=2, str=ma}

             {index=3, str=ora}

             {index=4, str=pass}

             {index=5, str=grape}

            */

        }

    }

}