Select

Learn to transform each element with Select.

Transforming with Select

The Select method transforms each element of a collection. It takes a lambda and produces a new value for each element. The result is a new collection of transformed elements; the original is unchanged.

Example: numbers.Select(n => n * n) squares each number. words.Select(w => w.ToUpper()) uppercases each word. Select is the C# equivalent of the map operation and is used to reshape data.

Chaining Where and Select

You can chain LINQ methods: apply one method to the result of another. Order matters: first filter with Where, then transform with Select. numbers.Where(n => n > 2).Select(n => n * 10) first keeps numbers greater than 2, then multiplies each by 10.

Chaining builds a readable pipeline. Each method returns an IEnumerable<T>; the next method applies to that. End with .ToList() or a foreach loop.

Exercise Compute squares and print

Compute the square of each number in numbers with Select and print each in a foreach loop. Square: n * n.

Show example solution

Generate squares with numbers.Select(n => n * n), loop with foreach, print with Console.WriteLine(s).
Example solution:
using System;
using System.Linq;

class Program
{
    static void Main()
    {
        int[] numbers = { 2, 3, 4 };
        foreach (var s in numbers.Select(n => n * n))
        {
            Console.WriteLine(s);
        }
    }
}

Test yourself

Match Select to its result

Select(n => n * 2)

Double
Select(n => n * n)

Square
Select(w => w.ToUpper())

UPPERCASE
Select(s => s.Length)

Length

Complete the Select body

var squares = numbers.Select(n => n ____ n);

Show answer

var squares = numbers.Select(n => n * n);

What does Select return?
```
var r = words.Select(w => w.Length);
```
- IEnumerable<int>
- IEnumerable<string>
- int
- string
Show answer

IEnumerable<int> — Correct. Select produces a new collection typed by the lambda's return value; Length is int, so it returns IEnumerable<int>.

Next lesson: OrderBy

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