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:

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// 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);
    }
}

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Output:


8
5
5
5



Example 2:











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// 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); 


    } 


} 



















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Output:


16
9
9
9
9
0



Reference:






    

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