Check whether a SortedList object contains a specific key in C#?

To check whether a SortedList object contains a specific key in C#, you use the Contains() method. This method returns true if the key exists in the SortedList, otherwise false. A SortedList automatically maintains its elements in sorted order by key.

Syntax

Following is the syntax for checking if a key exists in a SortedList −

bool result = sortedList.Contains(key);

Parameters

• key: The key to search for in the SortedList. The key can be of any type that implements IComparable.

Return Value

The Contains() method returns a bool value −

• true if the key is found in the SortedList

• false if the key is not found in the SortedList

Using Contains() Method

Example 1 - Basic Key Checking

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      SortedList list = new SortedList();
      list.Add("A", "Books");
      list.Add("B", "Electronics");
      list.Add("C", "Appliances");
      list.Add("D", "Pet Supplies");
      list.Add("E", "Clothing");
      list.Add("F", "Footwear");
      
      Console.WriteLine("Value associated with key E = " + list["E"]);
      list["E"] = "HDD";
      Console.WriteLine("Value associated with key E [Updated] = " + list["E"]);
      Console.WriteLine("Does the list has key C? = " + list.Contains("C"));
   }
}

The output of the above code is −

Value associated with key E = Clothing
Value associated with key E [Updated] = HDD
Does the list has key C? = True

Example 2 - Multiple Key Checks

using System;
using System.Collections;

public class Demo {
   public static void Main(String[] args) {
      SortedList sortedList = new SortedList();
      sortedList.Add("A", "1");
      sortedList.Add("B", "2");
      sortedList.Add("C", "3");
      sortedList.Add("D", "4");
      sortedList.Add("E", "5");
      sortedList.Add("F", "6");
      sortedList.Add("G", "7");
      sortedList.Add("H", "8");
      sortedList.Add("I", "9");
      sortedList.Add("J", "10");
      
      Console.WriteLine("SortedList elements...");
      foreach(DictionaryEntry d in sortedList) {
         Console.WriteLine("Key = " + d.Key + ", Value = " + d.Value);
      }
      Console.WriteLine("Count of SortedList key-value pairs = " + sortedList.Count);
      
      sortedList.RemoveAt(3);
      Console.WriteLine("\nEnumerator to iterate through the SortedList...");
      IDictionaryEnumerator demoEnum = sortedList.GetEnumerator();
      while (demoEnum.MoveNext())
         Console.WriteLine("Key = " + demoEnum.Key + ", Value = " + demoEnum.Value);
      Console.WriteLine("Count of SortedList key-value pairs (Updated) = " + sortedList.Count);
      
      Console.WriteLine("\nDoes the list has key C? = " + sortedList.Contains("C"));
      Console.WriteLine("Does the list has key M? = " + sortedList.Contains("M"));
   }
}

The output of the above code is −

SortedList elements...
Key = A, Value = 1
Key = B, Value = 2
Key = C, Value = 3
Key = D, Value = 4
Key = E, Value = 5
Key = F, Value = 6
Key = G, Value = 7
Key = H, Value = 8
Key = I, Value = 9
Key = J, Value = 10
Count of SortedList key-value pairs = 10

Enumerator to iterate through the SortedList...
Key = A, Value = 1
Key = B, Value = 2
Key = C, Value = 3
Key = E, Value = 5
Key = F, Value = 6
Key = G, Value = 7
Key = H, Value = 8
Key = I, Value = 9
Key = J, Value = 10
Count of SortedList key-value pairs (Updated) = 9

Does the list has key C? = True
Does the list has key M? = False

Key Points

• The Contains() method performs a binary search since SortedList maintains sorted order, making it efficient with O(log n) time complexity.

• Key comparison is case-sensitive for string keys.

• The method only checks for keys, not values. Use ContainsValue() to check for values.

• SortedList automatically sorts keys when new elements are added or existing ones are modified.

Conclusion

The Contains() method provides an efficient way to check if a specific key exists in a SortedList. It returns a boolean value indicating the presence of the key and uses binary search for optimal performance due to the sorted nature of the collection.