How to Use LINQ ToList in C# - Simple Guide

In C#, use ToList() from LINQ to convert an IEnumerable or query result into a List. This method creates a new list containing all elements from the source sequence, allowing easy access and modification.

Syntax

The ToList() method is called on an IEnumerable or LINQ query result to create a List of the same type.

Syntax:

var list = sourceSequence.ToList();

Here:

• sourceSequence is any collection or LINQ query result.
• ToList() converts it into a List.
• list is the new List containing all elements.

csharp

var list = sourceSequence.ToList();

Example

This example shows how to use ToList() to convert an array filtered by LINQ into a list, then print each item.

csharp

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

class Program
{
    static void Main()
    {
        int[] numbers = { 1, 2, 3, 4, 5, 6 };

        // Use LINQ to select even numbers and convert to List
        List<int> evenNumbers = numbers.Where(n => n % 2 == 0).ToList();

        // Print each even number
        foreach (int num in evenNumbers)
        {
            Console.WriteLine(num);
        }
    }
}

Output

2
4
6

Common Pitfalls

Common mistakes when using ToList() include:

• Calling ToList() unnecessarily on a list, causing extra copying.
• Forgetting to include using System.Linq;, which is required for LINQ methods.
• Assuming ToList() modifies the original collection (it creates a new list instead).

csharp

using System;
using System.Collections.Generic;
// Missing using System.Linq; causes error

class Program
{
    static void Main()
    {
        int[] numbers = { 1, 2, 3 };

        // This will cause a compile error without System.Linq
        // List<int> list = numbers.ToList();

        // Correct way:
        // Add 'using System.Linq;' at the top
    }
}

Quick Reference

LINQ ToList() Quick Tips:

• Use ToList() to get a List from any IEnumerable.
• Remember to add using System.Linq; to access LINQ methods.
• ToList() creates a new list; original data stays unchanged.
• Use it when you need to modify or index the collection.

Key Takeaways

Use ToList() to convert LINQ query results or IEnumerable to a List for easy access and modification.

Always include 'using System.Linq;' to use ToList() and other LINQ methods.

ToList() creates a new list and does not change the original collection.

Avoid unnecessary ToList() calls to prevent extra memory use.

Use ToList() when you need a concrete list instead of a lazy query.