dictionary-keyvaluepair

C# – Get dictionary key by value

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Dictionaries have keys mapped to values, which enables you to efficiently lookup values by key. But you can also do a reverse lookup: get the key associated with a value. The simplest option is to use FirstOrDefault(), but that’s only a good idea if you know the value exists for sure. Instead, the best option … 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# – How to sort a dictionary

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Dictionaries are unordered data structures. Key/value pairs aren’t stored in sorted order. When you want the Dictionary in sorted order, there are two simple options: I’ll show both options. Sort Dictionary with OrderBy() Use OrderBy() (from System.Linq) to sort the Dictionary by key or value. It returns the Dictionary’s KeyValuePairs in ascending sorted order. I’ll … 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# – Get key with the max value in a dictionary

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The simplest way to get the key with the max value in a dictionary is to use the Linq MaxBy() method (added in .NET 6). This returns the key/value pair with the max value. Here’s an example: Note: All examples shown initialize the dictionary with a small number of key/value pairs for readability. This outputs … Read more

C# – Loop through a dictionary

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The simplest way to loop through a dictionary is with a foreach loop. Here’s an example of initializing a dictionary with values and then looping through it: This outputs the following: The loop variable is a KeyValuePair<string, int> with Key and Value properties. Instead of using this, you can deconstruct the KeyValuePair into named variables, … Read more

C# – Merge two dictionaries in-place

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When you merge two dictionaries, you can either merge them in-place, or create a new dictionary and copy the values over to it. The following extension method does an in-place merge of two dictionaries. It loops through items in the right dictionary, adding them to the left dictionary. When duplicate keys exist, it’s keeping the … Read more