C# |用谓词
定义的条件从哈希集中移除元素
原文:https://www . geesforgeks . org/c-sharp-remove-elements-from-a-hashset-with-conditions-由谓词定义/
一个 HashSet 是一个独特元素的无序集合。它属于体系。集合.通用命名空间。它用于我们希望防止在集合中插入重复项的情况。就性能而言，与列表相比更好。
HashSet < T >。RemoveWhere(谓词< T > ) 方法用于从 HashSet < T >集合中移除所有与指定谓词定义的条件相匹配的元素。
语法:
public int RemoveWhere (Predicate<T> match);
返回值:这个方法返回从 HashSet < T >集合中移除的元素数量。
异常:如果匹配为空，该方法将给出参数异常。
注意:调用这个方法是一个 O(n)运算，其中 n 是 Count，即集合中包含的元素个数。
以下是说明使用 HashSet < T >的程序。移除 Where(谓词< T >)方法:
例 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);
}
}
Output:
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
例 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));
}
}
Output:
Number of elements are : 20
Number of elements are : 16
参考:
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