How to Create a Deep Copy of a List in C#?

Deep Copying Lists in C#

Directly assigning a list in C# (e.g., List<T> list2 = list1;) or using List<T> list2 = new List<T>(list1); creates a shallow copy. Modifications to one list affect the other because they share the same underlying objects. To create a true deep copy, where changes to one list are independent of the other, you need to duplicate the contained objects. Here's how:

Method 1: Using LINQ (Recommended)

The most concise and efficient approach utilizes LINQ's Select method to create new instances of each object within the list:

<code class="language-csharp">List<Book> books_2 = books_1.Select(book => new Book(book.title)).ToList();</code>

This line iterates through books_1, creates a new Book object for each element using the existing title (assuming your Book class has a constructor that takes the title), and then converts the resulting sequence back into a new List<Book>.

Method 2: Using ConvertAll (Alternative)

The ConvertAll method offers a slightly simpler syntax for the same outcome:

<code class="language-csharp">List<Book> books_2 = books_1.ConvertAll(book => new Book(book.title));</code>

This achieves the same deep copy as the LINQ approach. Choose whichever method you find more readable.

Both methods ensure that books_2 is a completely independent deep copy of books_1. Any changes made to either list will not affect the other. Remember that this assumes your Book class (or whatever type your list contains) has a suitable constructor to facilitate the creation of new instances. If your Book class has more properties, you'll need to include them in the new Book(...) constructor call accordingly.

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