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C# – Convert a dictionary to a list

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The simplest way to convert a dictionary to a list is by using the Linq ToList() method, like this: When used on a dictionary, ToList() returns a list of KeyValuePair objects. This example outputs the following: Dictionary keys to list If you want a list of the dictionary’s keys, use ToList() on Dictionary.Keys, like this: … Read more

C# – Remove duplicates from a list

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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

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There are two ways to iterate through a List<T> and remove items based on a condition: These remove items from the list in an in-place manner (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 … Read more

C# – Remove items from a list

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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# – Convert string list to int list

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You can convert a list of strings to a list of integers by using int.Parse() on all of the strings. There are two simple ways to do this: I’ll show examples of these using these methods and then explain how to handle parsing exceptions. Option 1 – Use List.ConvertAll() Here’s an example of how to … Read more

C# – How to disable ModelStateInvalidFilter

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There are two options for disabling ModelStateInvalidFilter: You’d do this when you want to manually perform model validation. I’ll show both options below. Disable ModelStateInvalidFilter globally To disable ModelStateInvalidFilter for *all* actions, set SuppressModelStateInvalidFilter=true in ConfigureApiBehaviorOptions, like this: Disable ModelStateInvalidFilter for specific actions To disable ModelStateInvalidFilter selectively, you can implement an IActionModelConvention attribute that removes … Read more

C# – Deserialize a JSON array to a list

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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# – Examples of using GroupBy() (Linq)

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Here’s an example of using the Linq GroupBy() method to group coders by language: This example outputs the following: GroupBy() produces groups that contain the grouping key (i.e. Language) and the list of objects in the group (i.e. the Coder objects). The GroupBy() syntax is complex because it supports many scenarios. You can select one … Read more

Multithreaded quicksort in C#

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One day I decided to challenge myself by trying to implement multithreaded quicksort. I wanted to see how it would compare to the built-in Array.Sort() method. I came up with two algorithms that were 2-4x faster than Array.Sort(): After continuing to tinker, in attempts to further optimize, I came across the AsParallel().OrderBy() method (PLINQ). After … Read more

C# – Parsing CSV data when a field has commas

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When you have commas in your CSV fields, it creates a conflict with the field delimiting commas. In other words, you can’t tell which data belongs to which field. How you deal with this will depend on one question: is the field with the comma enclosed in quotes? Comma is enclosed in quotes Spreadsheet programs … Read more