C# – Using String.Join()

You can use String.Join() to convert a collection of items to a string with a separator (such as a comma). Here’s an example of using String.Join() to convert a List of strings to a comma-separated string: This results in the following comma-separated string: String.Join() can be used on wide variety of input: I’ll show a … Read more

C# – Convert a List to a string

There are two good ways to convert a List<T> to a string: I’ll show examples of both approaches. Using String.Join() String.Join() is the simplest way to convert a List to a string. With this method, you pass in the List and a delimiter and it outputs a string. You can use any delimiter you want. … Read more

C# – How to use LinkedList

LinkedList<T> is a doubly linked list. It consists of nodes with values (i.e. integers, strings, etc…) and links to the next and previous node. LinkedList<T> has a reference to the head and tail nodes, which enables efficient insertion (and removal) from the start and end of the list. The main reason to use LinkedList<T> is … Read more

C# – Remove duplicates from a list

The simplest (and most efficient) way to remove duplicates from a list is by iterating, keeping track of items you’ve seen with a HashSet, and discarding items you’ve already seen. I’ll show four ways to implement this O(n) algorithm. At the end, I’ll explain a few inefficient approaches to avoid. Remove duplicates with ToHashSet() and … Read more

C# – Remove items from a list while iterating

There are two ways to iterate through a List<T> and remove items based on a condition: These do in-place removal (i.e. modify the original list) and avoid the problems you run into when doing this incorrectly (such as using a foreach or looping forward). I’ll show examples below. Then I’ll compare the performance. Option 1 … Read more

C# – Remove items from a list

Here are the different ways to remove items from a list: I’ll show examples of using these methods. Remove item by index with List.RemoveAt() You can use List.RemoveAt() to remove an item at an index (0-based). Here’s an example of removing the first and last item from the list: This removes the first item “A” … Read more

C# – How to add to a list

There are four ways to add items to a list: I’ll show examples of all of these methods for adding to a list. Append items with List.Add() You can use List.Add() to append an item to the end of the list. Here’s an example: This outputs the list’s contents: Initialize a list with items You … Read more

C# – Convert an array to a list

The simplest way to convert an array to a list is with the ToList() Linq method: This outputs the following: The List<T> class stores data in a dynamically sized array. So converting an array to a list boils down to copying the array to the list’s internal array. That’s what ToList() does. It creates a … Read more

C# – Convert list to array

The simplest way to convert a list to an array is to use the List.ToArray() method: This outputs the following: Internally, the List<T> class stores elements in a dynamically sized array (it resizes when necessary). So under the hood, List.ToArray() uses Array.Copy() to copy the list’s internal array to a new array. This is very … Read more

C# – How to sort a list

When you need to sort a list, you don’t need to reinvent the wheel. You can use one of these three built-in methods for sorting a list: In this article, I’ll show examples of using these three approaches for sorting a list. Sort a list with OrderBy() (Linq) The OrderBy() Linq method generates an IOrderedEnumerable … Read more

C# – Using a list of tuples

Here’s an example of how to initialize a list of named tuples: This creates a list of named value tuples (ValueTuple<string, int>) using list initializer syntax and then loops through the tuples. I suggest always using named value tuples (not System.Tuple). This outputs the following: I’ll now show how to add to the list of … Read more

C# – Parse a comma-separated string into a list of integers

Let’s say you want to parse a comma-separated string into a list of integers. For example, you have “1,2,3” and you want to parse it into [1,2,3]. This is different from parsing CSV with rows of comma-separated values. This is more straightforward. You can use string.Split(“,”) to get the individual values and then convert them … Read more

C# – Deserialize a JSON array to a list

When you’re working with a JSON array, you can deserialize it to a list like this: This deserializes all of the objects in the JSON array into a List<Movie>. You can use this list object like usual. Note: All examples will use System.Collections.Generic and System.Text.Json. I’ll exclude the using statements for brevity. Example – JSON … Read more

C# – Convert a list to a dictionary

The simplest way to convert a list to a dictionary is to use the Linq ToDictionary() method: This loops through the list and uses the key/element selector lambdas you passed in to build the dictionary. In this article, I’ll go into details about how to use ToDictionary() and show how to deal with duplicate keys. … Read more

Collection was modified; enumeration operation may not execute

If you try to add/remove items from a collection while it’s being looped over in a foreach loop (enumerated), then you’ll get the following exception: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.at System.Collections.Generic.List`1.Enumerator.MoveNext() This error can happen in two scenarios: The solution to this problem depends on which scenario you’re in. In this … Read more