Dictionary.Clear Method in C#

The Dictionary.Clear() method in C# removes all key/value pairs from the Dictionary<TKey,TValue>. This method is useful when you need to empty a dictionary completely while keeping the dictionary object itself for future use.

Syntax

public void Clear();

Parameters

The Clear() method takes no parameters.

Return Value

The Clear() method does not return any value. It has a void return type.

Using Dictionary.Clear() Method

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Dictionary<string, string> dict = new Dictionary<string, string>();
      
      dict.Add("One", "John");
      dict.Add("Two", "Tom");
      dict.Add("Three", "Jacob");
      dict.Add("Four", "Kevin");
      dict.Add("Five", "Nathan");
      
      Console.WriteLine("Count of elements = " + dict.Count);
      Console.WriteLine("\nKey/value pairs...");
      foreach(KeyValuePair<string, string> res in dict) {
         Console.WriteLine("Key = {0}, Value = {1}", res.Key, res.Value);
      }
      
      dict.Clear();
      Console.WriteLine("Cleared Key/value pairs...");
      foreach(KeyValuePair<string, string> res in dict) {
         Console.WriteLine("Key = {0}, Value = {1}", res.Key, res.Value);
      }
      Console.WriteLine("Count of elements now = " + dict.Count);
   }
}

The output of the above code is −

Count of elements = 5

Key/value pairs...
Key = One, Value = John
Key = Two, Value = Tom
Key = Three, Value = Jacob
Key = Four, Value = Kevin
Key = Five, Value = Nathan
Cleared Key/value pairs...
Count of elements now = 0

Clear vs. Reassignment

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Dictionary<int, string> numbers = new Dictionary<int, string>();
      
      numbers.Add(1, "One");
      numbers.Add(2, "Two");
      numbers.Add(3, "Three");
      
      Console.WriteLine("Original Count: " + numbers.Count);
      
      // Using Clear() method
      numbers.Clear();
      Console.WriteLine("After Clear(): " + numbers.Count);
      
      // Dictionary can be reused after Clear()
      numbers.Add(10, "Ten");
      numbers.Add(20, "Twenty");
      Console.WriteLine("After adding new elements: " + numbers.Count);
      
      foreach(var pair in numbers) {
         Console.WriteLine("Key = {0}, Value = {1}", pair.Key, pair.Value);
      }
   }
}

The output of the above code is −

Original Count: 3
After Clear(): 0
After adding new elements: 2
Key = 10, Value = Ten
Key = 20, Value = Twenty

Common Use Cases

• Resetting a cache − Clear all cached data before repopulating.

• Memory management − Remove all references to help garbage collection.

• Reusing dictionaries − Empty a dictionary for reuse in loops or different contexts.

• State management − Reset application state stored in dictionaries.

Conclusion

The Dictionary.Clear() method efficiently removes all key-value pairs from a dictionary, setting its count to zero while keeping the dictionary object intact for future use. This method is essential for scenarios requiring complete dictionary reset without creating new dictionary instances.