System.Linq.Enumerable.Select Method

Overview
Syntax
Parameters
Return Value
Remarks
Example

Overview

Projects each element of a sequence into a new form.

This is a LINQ extension method for IEnumerable<TSource>.

Syntax

public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)

public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, int, TResult> selector)

Parameters

Overload 1: `Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)`

source: IEnumerable<TSource>
A sequence of values to invoke a transform expression on.
selector: Func<TSource, TResult>
A transform function to apply to each element of the source sequence; the second parameter of the function is the index of the source element.

Overload 2: `Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, int, TResult> selector)`

source: IEnumerable<TSource>
A sequence of values to invoke a transform expression on.
selector: Func<TSource, int, TResult>
A transform function to apply to each element of the source sequence; the second parameter of the function is the index of the source element.

Return Value

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

Remarks

The Select method transforms each element in a sequence and returns a new sequence containing the transformed elements. This method does not modify the original sequence.

There are two overloads for the Select method:

The first overload takes a selector function that transforms each element without considering its index.
The second overload takes a selector function that transforms each element while also providing the index of the element to the function.

This method supports deferred execution, meaning that the transformation is not performed until the sequence is iterated over.

Example

Example 1: Basic usage

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

public class Example
{
    public static void Main(string[] args)
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };

        // Transform each number into its square
        IEnumerable<int> squares = numbers.Select(n => n * n);

        Console.WriteLine("Squares of numbers:");
        foreach (int square in squares)
        {
            Console.Write(square + " "); // Output: 1 4 9 16 25
        }
        Console.WriteLine();
    }
}
                        
                    

Example 2: Using index

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

public class Example
{
    public static void Main(string[] args)
    {
        List<string> words = new List<string> { "apple", "banana", "cherry" };

        // Transform each word into a string including its index
        IEnumerable<string> indexedWords = words.Select((word, index) => $"{index}: {word}");

        Console.WriteLine("Indexed words:");
        foreach (string indexedWord in indexedWords)
        {
            Console.WriteLine(indexedWord);
            // Output:
            // 0: apple
            // 1: banana
            // 2: cherry
        }
    }
}
                        
                    