C# | List.TrimExcess Method

List<T>.TrimExcess Method is used to set the capacity to the actual number of elements in the List<T>, if that number is less than a threshold value.

Syntax:

public void TrimExcess ();

Note:

This method can be used to minimize a collection’s memory overhead if no new elements will be added to the collection.
To reset a List<T> to its initial state, call the Clear method before calling TrimExcess method.
Trimming an empty List<T> sets the capacity of the List<T> to the default capacity.
The cost of reallocating and copying a large List<T> can be considerable, however, so the TrimExcess method does nothing if the list is at more than 90 percent of capacity. This avoids incurring a large reallocation cost for a relatively small gain.
This method is an O(n) operation, where n is Count.

Below programs illustrate the use of List<T>.TrimExcess Method:

Example 1:

// C# code to set the capacity to the 
// actual number of elements in the List 

using System; 

using System.Collections.Generic; 

class GFG { 

    // Driver code 

    public static void Main() 

    { 

        // Creating a List of strings 

        List<string> mylist = new List<string>(); 

        // Inserting elements into List 

        mylist.Add("1"); 

        mylist.Add("2"); 

        mylist.Add("3"); 

        mylist.Add("4"); 

        mylist.Add("5"); 

        // To  display the capacity of list 

        Console.WriteLine(mylist.Capacity); 

        // To display number of elements in List 

        Console.WriteLine(mylist.Count); 

        // using TrimExcess method 

        mylist.TrimExcess(); 

        // To  display the capacity of list 

        Console.WriteLine(mylist.Capacity); 

        // To display number of elements in List 

        Console.WriteLine(mylist.Count); 

    } 
}

Output:

Example 2:

// C# code to set the capacity to the 
// actual number of elements in the List 

using System; 

using System.Collections.Generic; 

class GFG { 

    // Driver code 

    public static void Main() 

    { 

        // Creating a List of integers 

        List<int> mylist = new List<int>(); 

        // Inserting elements into List 

        mylist.Add(45); 

        mylist.Add(78); 

        mylist.Add(32); 

        mylist.Add(231); 

        mylist.Add(123); 

        mylist.Add(76); 

        mylist.Add(726); 

        mylist.Add(716); 

        mylist.Add(876); 

        // To  display the capacity of list 

        Console.WriteLine(mylist.Capacity); 

        // To display number of elements in List 

        Console.WriteLine(mylist.Count); 

        // using TrimExcess method 

        mylist.TrimExcess(); 

        // To  display the capacity of list 

        Console.WriteLine(mylist.Capacity); 

        // To display number of elements in List 

        Console.WriteLine(mylist.Count); 

        // using clear method 

        mylist.Clear(); 

        // To  display the capacity of list 

        Console.WriteLine(mylist.Capacity); 

        // To display number of elements in List 

        Console.WriteLine(mylist.Count); 

    } 
}