linq-tolist

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 items from dictionary

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Dictionaries contain key/value pairs. When you want to remove one or more items from a dictionary, you can use one of the following methods: I’ll show examples below. Remove item by key Use Dictionary.Remove() to remove an item based on its key. If the key exists, it removes the key/value pair from the dictionary and … 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# – 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# – Convert an array to a list

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The simplest way to convert an array to a list is with the ToList() Linq method: This outputs the following: Besides using ToList(), you can also use the list constructor or AddRange(). Before I show those, I’ll explain why you’d want to use these special methods instead of just adding items individually to a new … Read more

C# – How to sort a list

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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

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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

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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 string values and then convert … Read more

C# – Parsing a CSV file

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In this article, I’ll show how to parse a CSV file manually and with a parser library (CsvHelper). Let’s say you have the following CSV file: To manually parse this, read the file line by line and split each line with a comma. This gives you a string array containing the fields that you can … Read more

C# – Filter a dictionary

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The simplest way to filter a dictionary is by using the Linq Where() + ToDictionary() methods. Here’s an example: Note: You can use the Dictionary constructor (new Dictionary<string, int>(filterList)) instead of ToDictionary() if you prefer. This produces a new dictionary with the filtered item: Where() produces a list (actually an IEnumerable) of KeyValuePair objects. Most … Read more

C# – Change a dictionary’s values in a foreach loop

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In .NET 5 and above, you can loop through a dictionary and directly change its values. Here’s an example: This outputs the following: You couldn’t do this before .NET 5, because it would invalidate the enumerator and throw an exception: InvalidOperationException: Collection was modified; enumeration operation my not execute. Instead, you’d have to make the … Read more

C# – Save a list of strings to a file

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The simplest way to save a list of strings to a file is to use File.WriteAllLines(). This creates (or overwrites) the file and writes each string on a new line. The resulting file looks like this: Note: Showing non-printable newline characters \r\n for clarity. Specifying the separator character What if you want to separate each … Read more

Complex DataBinding accepts as a data source either an IList or an IListSource

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If you try to set a list control’s DataSource to a type it can’t handle, then you’ll get the following exception: System.ArgumentException: Complex DataBinding accepts as a data source either an IList or an IListSource. (Parameter ‘value’)at System.Windows.Forms.ListControl.set_DataSource(Object value) Note: This applies to all controls that subclass ListControl, such as ComboBox and ListBox. This is … Read more

C# – Convert a list of strings into a set of enums

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Let’s say you have a list of HTTP status codes that you read in when the service starts up (perhaps from appsettings.json or from the database). Whenever you send an HTTP request, you want to check if the returned status code is in this list of status code. To make things more efficient, you want … 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