C# Dictionary: Get Value by Key

In C#, the Dictionary<TKey, TValue> class stores key-value pairs and provides efficient access to values through their associated keys. This collection, found in the System.Collections.Generic namespace, allows direct retrieval of values by key. This article explains various ways to retrieve values from a dictionary in C#.

Retrieving Values by Key

Using Indexer Syntax

The most straightforward way to get a value by key is to use the indexer syntax. However, if the key does not exist, it will throw a KeyNotFoundException.

using System;
using System.Collections.Generic;

public class DictionaryIndexerExample
{
    public static void Main()
    {
        // Create a dictionary with string keys and integer values
        Dictionary<string, int> ages = new Dictionary<string, int>
        {
            { "Alice", 25 },
            { "Bob", 30 },
            { "Charlie", 35 }
        };

        // Retrieve a value using the indexer syntax
        int bobAge = ages["Bob"];
        Console.WriteLine($"Bob's age: {bobAge}");

        // This line will throw an exception if the key "Dave" doesn't exist
        try
        {
            int daveAge = ages["Dave"];
        }
        catch (KeyNotFoundException)
        {
            Console.WriteLine("Key 'Dave' not found.");
        }
    }
}

Using TryGetValue

To safely retrieve a value without exceptions, use the TryGetValue method. It returns true if the key exists and false otherwise.

using System;
using System.Collections.Generic;

public class DictionaryTryGetValueExample
{
    public static void Main()
    {
        // Create a dictionary with string keys and integer values
        Dictionary<string, int> scores = new Dictionary<string, int>
        {
            { "Alice", 85 },
            { "Bob", 90 },
            { "Charlie", 95 }
        };

        // Try to get a value by key using TryGetValue
        if (scores.TryGetValue("Charlie", out int charlieScore))
        {
            Console.WriteLine($"Charlie's score: {charlieScore}");
        }
        else
        {
            Console.WriteLine("Key 'Charlie' not found.");
        }

        // Attempt to retrieve a non-existent key
        if (!scores.TryGetValue("Dave", out int daveScore))
        {
            Console.WriteLine("Key 'Dave' not found.");
        }
    }
}

Summary of Key Methods

Indexer Syntax (dictionary[key]): Directly retrieves a value but throws an exception if the key isn't found.
TryGetValue: Safely retrieves a value and avoids exceptions by returning a boolean status.
ContainsKey: Checks for the existence of a key before accessing it.

Best Practices

Use TryGetValue: Use TryGetValue instead of indexer syntax to handle missing keys gracefully.
Key Type: Ensure the key type provides a good hash code implementation for consistent behavior.

Conclusion

Retrieving values from a C# dictionary is straightforward, and understanding the appropriate methods helps prevent errors and maintain efficient code. The TryGetValue method is the best practice for accessing values safely, while the indexer syntax is quicker when the existence of a key is known.

c# dictionary get value by key