Check if value already exists in a Dictionary in C#

This post will discuss how to check whether a specific value already exists in a Dictionary<TKey,TValue> in C#.

1. Using `Dictionary<TKey,TValue>.ContainsValue()` method

The Dictionary<TKey,TValue> class contains the ContainsValue() method, which checks if it contains a specific value or not. It returns a boolean value to indicate the value is found or not.

using System;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

Dictionary<string, string> dict = new Dictionary<string, string>();

dict.Add("White", "#FFFFFF");

dict.Add("Grey", "#808080");

dict.Add("Silver", "#C0C0C0");

dict.Add("Black", "#000000");

boolean valueExists = dict.ContainsValue("#C0C0C0");

Console.WriteLine(valueExists); // True

}

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Alternatively, you can use the ContainsKey() method to check if a Dictionary<TKey,TValue> contains a specific key.

using System;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

Dictionary<string, string> dict = new Dictionary<string, string>();

dict.Add("White", "#FFFFFF");

dict.Add("Grey", "#808080");

dict.Add("Silver", "#C0C0C0");

dict.Add("Black", "#000000");

boolean keyExists = dict.ContainsValue("Silver");

Console.WriteLine(keyExists); // True

}

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2. Using `Enumerable.Any()` method

The Any() method returns true if any element of the sequence satisfies the provided condition. To check whether a value exists in a dictionary, you can use it like below. Note that you need to include the System.Linq namespace.

using System;

using System.Linq;

using System.Collections.Generic;

public static class Extensions

{

public static bool hasValue<K,V>(this IDictionary<K,V> dict, V value)

{

return dict.Any(kvp => kvp.Value.Equals(value));

}

public class Example

{

public static void Main()

{

Dictionary<string, string> dict = new Dictionary<string, string>();

dict.Add("White", "#FFFFFF");

dict.Add("Grey", "#808080");

dict.Add("Silver", "#C0C0C0");

dict.Add("Black", "#000000");

boolean valueExists = dict.hasValue("#C0C0C0");

Console.WriteLine(valueExists); // True

}

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3. Using Custom Routine

The more traditional approach to finding a value in a dictionary involves iterating through the dictionary and checking each key-value pair for the matching value. In C#, this translates to:

using System;

using System.Collections.Generic;

public static class Extensions

{

public static bool hasValue<K,V>(this IDictionary<K,V> dict, V value)

{

foreach (KeyValuePair<K,V> kvp in dict)

{

if (kvp.Value.Equals(value)) {

return true;

}

return false;

}

public class Example

{

public static void Main()

{

Dictionary<string, string> dict = new Dictionary<string, string>();

dict.Add("White", "#FFFFFF");

dict.Add("Grey", "#808080");

dict.Add("Silver", "#C0C0C0");

dict.Add("Black", "#000000");

boolean valueExists = dict.hasValue("#C0C0C0");

Console.WriteLine(valueExists); // True

}

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The above solution iterates over the dictionary mappings using the foreach loop. You can directly iterate over all the values contained in the dictionary using the Dictionary<TKey,TValue>.Values property.

using System;

using System.Collections.Generic;

public static class Extensions

{

public static bool hasValue<K,V>(this IDictionary<K,V> dict, V value)

{

foreach(V v in dict.Values) {

if (v.Equals(value)) {

return true;

}

return false;

}

public class Example

{

public static void Main()

{

Dictionary<string, string> dict = new Dictionary<string, string>();

dict.Add("White", "#FFFFFF");

dict.Add("Grey", "#808080");

dict.Add("Silver", "#C0C0C0");

dict.Add("Black", "#000000");

boolean valueExists = dict.hasValue("#C0C0C0");

Console.WriteLine(valueExists); // True

}

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That’s all about checking whether a specific value already exists in a Dictionary<TKey,TValue> in C#.

Check if value already exists in a Dictionary in C#

1. Using Dictionary<TKey,TValue>.ContainsValue() method

2. Using Enumerable.Any() method

3. Using Custom Routine

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1. Using `Dictionary<TKey,TValue>.ContainsValue()` method

2. Using `Enumerable.Any()` method