C#HashSet教程展示了如何在C#中使用HashSet集合。
哈希集
HashSet表示一组值。它不包含重复元素。该集合对数学集合抽象进行建模。
HashSet不提供元素排序。如果我们需要保持顺序，我们可以使用SortedSet集合。
C#HashSet计数元素
Count属性返回HashSet中元素的数量。
var brands = new HashSet<string>();
brands.Add("Wilson");
brands.Add("Nike");
brands.Add("Volvo");
brands.Add("IBM");
brands.Add("IBM");
int nOfElements = brands.Count;
Console.WriteLine($"The set contains {nOfElements} elements");
Console.WriteLine(string.Join(", ", brands));
我们有一套品牌。
var brands = new HashSet<string>();
创建了一个新的HashSet。
brands.Add("Wilson");
使用Add方法将元素添加到集合中。
int nOfElements = brands.Count;
我们使用Count属性获取元素的数量。
$ dotnet run The set contains 4 elements Wilson, Nike, Volvo, IBM
C#HashSet删除元素
在下一个示例中，我们从HashSet中删除元素。
var brands = new HashSet<string>
{
"Wilson", "Nike", "Volvo", "Kia", "Lenovo"
};
Console.WriteLine(string.Join(", ", brands));
brands.Remove("Kia");
brands.Remove("Lenovo");
Console.WriteLine(string.Join(", ", brands));
brands.Clear();
if (brands.Count == 0)
{
Console.WriteLine("The brands set is empty");
}
var words = new HashSet<string>
{
"sky", "blue", "cup", "cold", "cloud", "pen", "bank"
};
words.RemoveWhere(word => word.Length == 3);
Console.WriteLine(string.Join(", ", words));
使用Remove、Clear和RemoveWhere删除元素。
brands.Remove("Kia");
使用Remove删除单个元素。
brands.Clear();
使用Clear删除所有元素。
words.RemoveWhere(word => word.Length == 3);
使用RemoveWhere，我们删除满足给定条件的元素。
$ dotnet run Wilson, Nike, Volvo, Kia, Lenovo Wilson, Nike, Volvo The brands set is empty blue, cold, cloud, bank
C#HashSet循环
我们可以使用foreach和while关键字遍历HashSet。
var words = new HashSet<string>
{
"sky", "blue", "cup", "cold", "cloud", "pen", "bank"
};
foreach (var word in words)
{
Console.WriteLine(word);
}
Console.WriteLine("----------------------");
var it = words.GetEnumerator();
while (it.MoveNext())
{
Console.WriteLine(it.Current);
}
在示例中，我们使用foreach和while遍历单词的HashSet。
$ dotnet run sky blue cup cold cloud pen bank ---------------------- sky blue cup cold cloud pen bank
C#HashSet包含
Contains方法确定HashSet是否包含指定的元素。
var words = new HashSet<string>
{
"sky", "blue", "cup", "cold", "cloud", "pen", "bank"
};
Console.WriteLine(words.Contains("sky"));
Console.WriteLine(words.Contains("water"));
Console.WriteLine("-----------------");
var users = new HashSet<User>
{
new User("John Doe", "gardener"),
new User("Roger Roe", "driver"),
new User("Lucy Smith", "teacher")
};
var u1 = new User("John Doe", "gardener");
var u2 = new User("Jane Doe", "student");
Console.WriteLine(users.Contains(u1));
Console.WriteLine(users.Contains(u2));
record User(string name, string occupation);
我们有两个HashSet集合。
var words = new HashSet<string>
{
"sky", "blue", "cup", "cold", "cloud", "pen", "bank"
};
Console.WriteLine(words.Contains("sky"));
Console.WriteLine(words.Contains("water"));
我们检查单词的HashSet是否包含这些指定的双词。
var u1 = new User("John Doe", "gardener");
var u2 = new User("Jane Doe", "student");
Console.WriteLine(users.Contains(u1));
Console.WriteLine(users.Contains(u2));
C#记录包含Equals和GetHashCode方法的默认实现；因此，Contains方法的工作方式与我们预期的一样。
$ dotnet run True False ----------------- True False
如果是类，我们需要实现Equals和GetHashCode方法。
var users = new HashSet<User>
{
new User("John Doe", "gardener"),
new User("Roger Roe", "driver"),
new User("Lucy Smith", "teacher")
};
var u1 = new User("John Doe", "gardener");
var u2 = new User("Jane Doe", "student");
Console.WriteLine(users.Contains(u1));
Console.WriteLine(users.Contains(u2));
class User
{
string Name { get; set; }
string Occupation { get; set; }
public User(string name, string occupation)
=> (Name, Occupation) = (name, occupation);
public override bool Equals(object obj)
{
return obj is User user &&
Name == user.Name;
}
public override int GetHashCode()
{
return HashCode.Combine(Name);
}
}
在这个例子中，我们有一个用户对象的HashSet。由于该对象是使用class关键字定义的，因此我们添加了Equals和GetHashCode方法的实现。
$ dotnet run True False
C#哈希集
HashSet包含一组特定于集合的方法。
var vals1 = new HashSet<int> { 1, 2, 3, 4, 5 };
var vals2 = new HashSet<int> { 6, 7, 8, 9, 10 };
vals1.UnionWith(vals2);
Console.WriteLine(string.Join(", ", vals1));
var vals3 = new HashSet<int> { 1, 2, 3, 4, 5 };
var vals4 = new HashSet<int> { 3, 4, 5, 6, 7 };
vals3.IntersectWith(vals4);
Console.WriteLine(string.Join(", ", vals3));
我们使用UnionWith和IntersectWith方法。
vals1.UnionWith(vals2);
UnionWith方法修改HashSet对象以包含来自两个集合的元素。
vals3.IntersectWith(vals4);
IntersectWith方法修改HashSet对象以包含存在于两个对象中的元素。
$ dotnet run 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 3, 4, 5
C#排序集
SortedSet表示一组未排序的对象。
var vals = new SortedSet<int> { 5, 2, 1, 4, 3, 7, 6 };
Console.WriteLine(string.Join(", ", vals));
var words = new SortedSet<string>
{
"sky", "blue", "cup", "cold", "cloud", "pen", "bank"
};
Console.WriteLine(string.Join(", ", words));
var users = new SortedSet<User>
{
new User("Robin", "bookseller"),
new User("John", "gardener"),
new User("John", "writer"),
new User("Janet", "teacher"),
new User("Andrew", "driver"),
new User("Lucy", "accountant")
};
Console.WriteLine(string.Join("\n", users));
record User(string Name, string Occupation) : IComparable<User>
{
public int CompareTo(User other)
{
return this.Occupation.CompareTo(other.Occupation);
}
}
我们有整数、字符串和用户的SortedSet。
$ dotnet run
1, 2, 3, 4, 5, 6, 7
bank, blue, cloud, cold, cup, pen, sky
User { Name = Lucy, Occupation = accountant }
User { Name = Robin, Occupation = bookseller }
User { Name = Andrew, Occupation = driver }
User { Name = John, Occupation = gardener }
User { Name = Janet, Occupation = teacher }
User { Name = John, Occupation = writer }
在本文中，我们使用了C#HashSet。
列出所有C#教程。
