How to Remove Key-Value Pairs from a Dictionary Based on Values in C#

How to Remove Key-Value Pairs from a Dictionary Based on Values in C# ?

Answer

To remove key-value pairs from a dictionary based on values in C#, you can use the `Remove` method in combination with a loop to identify and remove the pairs that match the specified value.


✐ Examples

1 Removing Key-Value Pairs Based on Values Using a Loop

We can remove key-value pairs from a dictionary in C# based on their values by using a loop to identify and remove pairs that match a specified value. This example demonstrates how to achieve this and print the dictionary contents before and after the removal.

For example,

  1. We start by including the necessary namespace: using System.Collections.Generic;.
  2. We declare and initialize a dictionary named myDictionary with integer keys and string values.
  3. We print the dictionary contents before removing key-value pairs.
  4. We use a loop to identify and remove pairs that match the specified value.
  5. We print the dictionary contents after removing the key-value pairs.

C# Program

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Declare and initialize a dictionary
        Dictionary<int, string> myDictionary = new Dictionary<int, string>
        {
            {1, "One"},
            {2, "Two"},
            {3, "Three"},
            {4, "Two"}
        };

        // Print the dictionary contents before removal
        Console.WriteLine("Dictionary contents before removal:");
        foreach (KeyValuePair<int, string> kvp in myDictionary)
        {
            Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
        }

        // Value to remove
        string valueToRemove = "Two";

        // Identify keys to remove
        List<int> keysToRemove = new List<int>();
        foreach (var kvp in myDictionary)
        {
            if (kvp.Value == valueToRemove)
            {
                keysToRemove.Add(kvp.Key);
            }
        }

        // Remove identified keys
        foreach (var key in keysToRemove)
        {
            myDictionary.Remove(key);
        }

        // Print the dictionary contents after removal
        Console.WriteLine("Dictionary contents after removal:");
        foreach (KeyValuePair<int, string> kvp in myDictionary)
        {
            Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
        }
    }
}

Output

Dictionary contents before removal:
Key: 1, Value: One
Key: 2, Value: Two
Key: 3, Value: Three
Key: 4, Value: Two
Dictionary contents after removal:
Key: 1, Value: One
Key: 3, Value: Three

2 Removing Key-Value Pairs Based on Values Using LINQ

We can remove key-value pairs from a dictionary in C# based on their values using LINQ to identify and remove pairs that match a specified value. This example demonstrates how to achieve this and print the dictionary contents before and after the removal.

For example,

  1. We start by including the necessary namespaces: using System.Collections.Generic; and using System.Linq;.
  2. We declare and initialize a dictionary named myDictionary with integer keys and string values.
  3. We print the dictionary contents before removing key-value pairs.
  4. We use LINQ to identify and remove pairs that match the specified value.
  5. We print the dictionary contents after removing the key-value pairs.

C# Program

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        // Declare and initialize a dictionary
        Dictionary<int, string> myDictionary = new Dictionary<int, string>
        {
            {1, "One"},
            {2, "Two"},
            {3, "Three"},
            {4, "Two"}
        };

        // Print the dictionary contents before removal
        Console.WriteLine("Dictionary contents before removal:");
        foreach (KeyValuePair<int, string> kvp in myDictionary)
        {
            Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
        }

        // Value to remove
        string valueToRemove = "Two";

        // Remove key-value pairs based on value using LINQ
        myDictionary = myDictionary
            .Where(kvp => kvp.Value != valueToRemove)
            .ToDictionary(kvp => kvp.Key, kvp => kvp.Value);

        // Print the dictionary contents after removal
        Console.WriteLine("Dictionary contents after removal:");
        foreach (KeyValuePair<int, string> kvp in myDictionary)
        {
            Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
        }
    }
}

Output

Dictionary contents before removal:
Key: 1, Value: One
Key: 2, Value: Two
Key: 3, Value: Three
Key: 4, Value: Two
Dictionary contents after removal:
Key: 1, Value: One
Key: 3, Value: Three

Summary

In this tutorial, we learned How to Remove Key-Value Pairs from a Dictionary Based on Values in C# language with well detailed examples.


More C# Dictionaries Tutorials

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  2. How to create a Dictionary with Initial Key-Value Pairs in C# ?
  3. How to Print a Dictionary in C# ?
  4. How to Add a Key-Value Pair to a Dictionary in C# ?
  5. How to Set a Default Value for a Key in a Dictionary in C# ?
  6. How to Update the Value for a Key in a Dictionary in C# ?
  7. How to Check if a Dictionary is Empty in C# ?
  8. How to Check if a Key Exists in a Dictionary in C# ?
  9. How to Check if a Value Exists in a Dictionary in C# ?
  10. How to Get the Value Associated with a Key in a Dictionary in C# ?
  11. How to Remove a Key-Value Pair from a Dictionary in C# ?
  12. How to Remove Key-Value Pairs from a Dictionary Based on Values in C# ?
  13. How to Clear all Key-Value Pairs from a Dictionary in C# ?
  14. How to Iterate over Keys in a Dictionary in C# ?
  15. How to Iterate over Values in a Dictionary in C# ?
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  17. How to Get the Size (Number of Key-Value Pairs) of a Dictionary in C# ?
  18. How to Convert a Dictionary to an Array of Keys in C# ?
  19. How to Convert a Dictionary to an Array of Values in C# ?
  20. How to Convert a Dictionary to an Array of Key-Value Pairs in C# ?
  21. How to Merge Two Dictionaries in C# ?
  22. How to Clone a Dictionary in C# ?
  23. How to Check if Two Dictionaries are Equal in C# ?
  24. How to Sort a Dictionary by Keys in C# ?
  25. How to Sort a Dictionary by Values in C# ?
  26. How to Filter a Dictionary Based on Keys in C# ?
  27. How to Filter a Dictionary Based on Values in C# ?
  28. How to Reduce Values in a Dictionary to a Single Value in C# ?
  29. How to Convert an Array of Key-Value Pairs to a Dictionary in C# ?
  30. How to Convert a Dictionary to a JSON String in C# ?
  31. How to Convert a JSON String to a Dictionary in C# ?
  32. How to Swap Keys and Values in a Dictionary in C# ?
  33. How to Create a Dictionary of Dictionaries in C# ?
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