HashSet<T>.RemoveWhere(Predicate<T>) Method

Definition

Namespace:

System.Collections.Generic

Assemblies:

netstandard.dll, System.Collections.dll

Source:

HashSet.cs

Removes all elements that match the conditions defined by the specified predicate from a HashSet<T> collection.

C#

public int RemoveWhere(Predicate<T> match);

Parameters

match

Predicate<T>

The Predicate<T> delegate that defines the conditions of the elements to remove.

Returns

Int32

The number of elements that were removed from the HashSet<T> collection.

Exceptions

ArgumentNullException

match is null.

Examples

The following example demonstrates how to remove values from a HashSet<T> collection using the Remove method. In this example, all odd integers are removed from the HashSet<T> collection as specified by the match delegate.

C#

HashSet<int> numbers = new HashSet<int>();

for (int i = 0; i < 20; i++) {
    numbers.Add(i);
}

// Display all the numbers in the hash table.
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

// Remove all odd numbers.
numbers.RemoveWhere(IsOdd);
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

// Check if the hash table contains 0 and, if so, remove it.
if (numbers.Contains(0)) {
    numbers.Remove(0);
}
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

bool IsOdd(int i)
{
    return ((i % 2) == 1);
}

void DisplaySet(HashSet<int> set)
{
    Console.Write("{");
    foreach (int i in set)
        Console.Write(" {0}", i);

    Console.WriteLine(" }");
}

// This example displays the following output:
//    numbers contains 20 elements: { 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 }
//    numbers contains 10 elements: { 0 2 4 6 8 10 12 14 16 18 }
//    numbers contains 9 elements: { 2 4 6 8 10 12 14 16 18 }

Remarks

Calling this method is an O(n) operation, where n is Count.

Applies to