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- The simplest way to convert a dictionary to a list is by using the Linq ToList () method, like this: using System.Collections.Generic; using System.Linq; var dictionary = new Dictionary ()
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How to create a dictionary from a list or array in C#?
How to convert a collection into a dictionary?
How to convert a dictionary to a list?
What is todictionary method in C#?
Aug 31, 2010 · The ToDictionary() method has an overload that takes two lambda expressions (nitpick: delegates); one for the key and one for the value. For example: var myDic = GetSomeStrings().ToDictionary(x => x, x => x.Number('A')); Note that the values returned by GetSomeStrings() must be unique.
Usage example
var myDic = GetSomeStrings().ToDictionary(x => x, x => x.Number('A'));Oct 12, 2023 · The simplest way to convert a dictionary to a list is by using the Linq ToList () method, like this: using System.Collections.Generic; using System.Linq; var dictionary = new Dictionary<int, string >() { [100] = "Bob" , [101] = "Linda" , [102] = "Teddy" };
- C# Dictionary Example
- Duplicate Values
- Iterate Over A Dictionary
- Get Keys and Values
- Internals
- Use Immutable Objects For Keys
- TryGetValue vs Containskey+Item
- Dictionary Exceptions
- Dictionary vs OrderedDictionary
- Dictionary vs SortedDictionary
Initialization
To initialize a dictionary in C#, we first need to provide the type for the key and the type for the value. For example, for a dictionary that stores the name and age of a person, the initialization would be: The first type inside the angle brackets is the key type. The second type is the value type.
Initial values
To define initial values at the time of initialization, we use the following syntax: The collection-initializersyntax above is like the initialization of an array. Another way to initialize a dictionary is object initializerintroduced in C# 6:
Add item to a dictionary
To add an item to a dictionary, we use the Add method. For example: This would add "Adam" and his age of 24 to the nameToAge dictionary.
In C#, a dictionary can only have one value for a key. If we add another value with the same key, then we'll get the KeyNotFoundExceptionexception. For example, if we try to add a value with key "Adam" then we would get: Here we get the exception because there is already a key "Adam" and the dictionary cannot have two values for the same key. As de...
To iterate over keys and values of a dictionary, we can use the foreach loop: The item variable is an object of type KeyValuePair which has the properties to provide the key and value. KeyValuePair is a very simple struct. It only holds two properties - Key and Value:
Dictionary exposes two read-only properties to get all keys or values: These properties are useful if we want to iterate over all keys or values of a dictionary.
C# dictionary uses a hash table as its internal data structure. Hash tables rely on hash codes to locate an item. For example, adding an item to a dictionary performs these 3 steps in the background: 1. Compute a hash code for the key. 2. Verify the key's hash code is not equal to the key already in the dictionary. 3. Place the entry in the hash ta...
A dictionary can break if we use a reference type as a key. That's because Dictionary stores a reference to that object and not the object itself. So if we change the object after adding it to the dictionary, then we would break the whole dictionary. Because of that, it's a best practice to use immutable objects, like strings, when using the dictio...
TryGetValue and ContainsKey are the two most popular ways of getting a value from a dictionary. For ContainsKey, it's a two-step process: 1. Do the lookup to verify the key exists in the dictionary. 2. Do the lookup to get the value from the dictionary based on the key. On the other hand, TryGetValue does the lookup and gets the value in one step. ...
These are the most common exceptions we can get from a dictionary: To prevent these exceptions, use TryGetValue and TryAdd.
The main difference between Dictionary and OrderedDictionary is that Dictionary does not guaranteethe order in which it will return values, but OrderedDictionary does. OrderedDictionary is less efficient than Dictionary because insert/delete operations have to be done on an array, with the complexity of O(n) at worst.
SortedDictionary is another class that implements IDictionary. The main difference between a Dictionary and SortedDictionary is that SortedDictionary uses a binary search tree with O(log n) retrieval, while Dictionary is a hash table of O(1) complexity for access. Use SortedDictionary if you have an extensive list of items and need them sorted.
public class Dictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyCollection<System.Collectio...
One such method is ToDictionary, which converts a collection into a Dictionary<TKey, TValue> based on a key selector function and an optional element selector function. The ToDictionary method in C# is a LINQ extension method that converts a sequence of elements (e.g., a collection or query result) into a dictionary.
Dec 8, 2023 · Introduction. Understanding C# Dictionary. Adding Elements to a Dictionary. Accessing Elements in a Dictionary. Modifying Elements in a Dictionary. Dealing with Errors and Exceptions. Conclusion. Introduction. C# is a powerful programming language, filled with numerous features. One such feature is the C# Dictionary.
Apr 21, 2023 · myDictionary.Add(1, "stuff"); myDictionary.TryAdd(1, "stuff"); // You only remove via the key myDictionary.Remove(1); myDictionary.Clear(); you can find items in a dictionary in a few different ways (though I'd probably avoid linq):
