C# | Remove elements from a HashSet with conditions defined by the predicate
A HashSet is an unordered collection of the unique elements. It comes under System.Collections.Generic namespace. It is used in a situation where we want to prevent duplicates from being inserted in the collection. As far as performance is concerned, it is better in comparison to the list.
HashSet<T>.RemoveWhere(Predicate<T>) method is used to remove all elements that match the conditions defined by the specified predicate from a HashSet<T> collection.
Syntax:
public int RemoveWhere (Predicate<T> match);
Return Value: This method returns the number of elements that were removed from the HashSet<T> collection.
Exception: This method will give the ArgumentNullException if the match is null.
Note: Calling this method is an O(n) operation, where n is Count i.e, the number of elements that are contained in the set.
Below are the programs to illustrate the use of HashSet<T>.RemoveWhere(Predicate<T>) Method:
Example 1:
// C# code to remove elements from a HashSet // with conditions defined by the predicate using System; using System.Collections.Generic; class GFG { // Driver code public static void Main() { // Creating a HashSet of integers HashSet< int > mySet = new HashSet< int >(); // Inserting elements into HashSet for ( int i = 0; i < 10; i++) { mySet.Add(i); } Console.WriteLine( "The elements in HashSet are : " ); // Displaying the elements in HashSet foreach ( int i in mySet) { Console.WriteLine(i); } // Displaying the number of elements in HashSet Console.WriteLine( "Number of elements are : " + mySet.Count); // Remove elements from a HashSet // with conditions defined by the predicate mySet.RemoveWhere(isEven); Console.WriteLine( "The elements in HashSet are : " ); // Displaying the elements in HashSet foreach ( int i in mySet) { Console.WriteLine(i); } // Displaying the number of elements in HashSet Console.WriteLine( "Number of elements are : " + mySet.Count); } // Helper function which tells // whether an element is even or not private static bool isEven( int i) { return ((i % 2) == 0); } } |
The elements in HashSet are : 0 1 2 3 4 5 6 7 8 9 Number of elements are : 10 The elements in HashSet are : 1 3 5 7 9 Number of elements are : 5
Example 2:
// C# code to remove elements from a HashSet // with conditions defined by the predicate using System; using System.Collections.Generic; class GFG { // Driver code public static void Main() { // Creating a HashSet of integers HashSet< int > mySet = new HashSet< int >(); // Inserting elements into HashSet for ( int i = 0; i < 20; i++) { mySet.Add(i); } // Displaying the number of elements in HashSet Console.WriteLine( "Number of elements are : " + mySet.Count); // Remove elements from a HashSet // with conditions defined by the predicate mySet.RemoveWhere(myFunc); // Displaying the number of elements in HashSet Console.WriteLine( "Number of elements are : " + mySet.Count); } // Helper function which tells // whether an element is divisible // by both 2 and 3 private static bool myFunc( int i) { return ((i % 2) == 0 && (i % 3 == 0)); } } |
Number of elements are : 20 Number of elements are : 16
Reference:
- https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.hashset-1.removewhere?view=netframework-4.7.2
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