4.排序操作符
OrderBy
作用：基于一个keySelector方法对输入序列进行排序，keySelector方法
将为每个输入元素返回一个键值，并会生成一个已排序的输出序列
IOrderedEnumerable<T>，这个输出序列将根据返回的键值按升序排列。
原型
public static IOrderedEnumerable<T> OrderBy<T, K>(
this IEnumerable<T> source,
Func<T, K> keySelector)
where
K:IComparable<K>;
public static IOrderedEnumerable<T> OrderBy<T, K>(
this IEnumerable<T> source,
Func<T, K> keySelector,
IComparable<K> comparer);
例子
static void Main(string[] args)
{
int[] items = { 12,23,1,56,3,10,100,32,9,15};
var result = items.OrderBy(c => c);
//显示查询结果
foreach (var item in result)
{
Console.WriteLine(item);
}
Console.Read();
}
结果
例子
public class Student
{
public int Id;
public string Name;
public int Age;
}
public class TestComparer : IComparer<int>
{
public int Compare(int x, int y)
{
if (x < y)
{
return (-1);
}
else if (x > y)
{
return (1);
}
else
{
return (0);
}
}
}
static void Main(string[] args)
{
List<Student> items = new List<Student>()
{
new Student{
Id = 1,
Name = "yxg1",
Age = 20
},
new Student{
Id = 2,
Name = "yxg2",
Age = 10
},
new Student{
Id = 3,
Name = "yxg3",
Age = 60
},
new Student{
Id = 4,
Name = "yxg4",
Age = 50
},
new Student{
Id = 5,
Name = "yxg5",
Age = 70
}
};
TestComparer t = new TestComparer();
var result = items.OrderBy(c => c.Age,t);
//显示查询结果
foreach (var item in result)
{
Console.WriteLine(item.Id + ":" + item.Name + ":" + item.Age);
}
Console.Read();
}
结果
OrderByDescending
作用： 和OrderBy相似，区别在于对序列中的元素进行降序排列。
原型：和OrderBy操作符相同
public static IOrderedEnumerable<T> orderByDescending<T, K>(
this IEnumerable<T> source,
Func<T, K> keySelector)
where
K: IComparable<K>;
public static IOrderedEnumerable<T> OrderBy<T, K>(
this IEnumerable<T> source,
Func<T, K> keySelector,
IComparable<K> comparer);
例子
static void Main(string[] args)
{
int[] items = { 12, 23, 1, 56, 3, 10, 100, 32, 9, 15 };
var result = items.OrderByDescending(c => c);
//显示查询结果
foreach (var item in result)
{
Console.WriteLine(item);
}
Console.Read();
}
结果
例子
public class Student
{
public int Id;
public string Name;
public int Age;
}
public class TestComparer : IComparer<int>
{
public int Compare(int x, int y)
{
if (x < y)
{
return (-1);
}
else if (x > y)
{
return (1);
}
else
{
return (0);
}
}
}
static void Main(string[] args)
{
List<Student> items = new List<Student>()
{
new Student{
Id = 1,
Name = "yxg1",
Age = 20
},
new Student{
Id = 2,
Name = "yxg2",
Age = 10
},
new Student{
Id = 3,
Name = "yxg3",
Age = 60
},
new Student{
Id = 4,
Name = "yxg4",
Age = 50
},
new Student{
Id = 5,
Name = "yxg5",
Age = 70
}
};
TestComparer t = new TestComparer();
var result = items.OrderByDescending(c => c.Age,t);
//显示查询结果
foreach (var item in result)
{
Console.WriteLine(item.Id + ":" + item.Name + ":" + item.Age);
}
Console.Read();
}
结果
ThenBy
作用：使用在OrderBy（OrderByDescending）操作符之后，输入序列根据keySelector方法
将返回一个键值进行排序，并将生成一个类型为IOrderedEnumerable<T>的已排序的输出序列
原型
public static IOrderedEnumerable<T> ThenBy<T, K>(
this IOrderedEnumerable<T> source,
Func<T, K> keySelector)
where
K : IComparable<K>;
public static IOrderedEnumerable<T> ThenBy<T, K>(
this IOrderedEnumerable<T> source,
Func<T, K> keySelector,
IComparer<K> comparer);
ThenByDescending
作用：和ThenBy相似，区别在于对序列中的元素进行降序排列。
原型
public static IOrderedEnumerable<T> ThenBy<T, K>(
this IOrderedEnumerable<T> source,
Func<T, K> keySelector)
where
K : IComparable<K>;
public static IOrderedEnumerable<T> ThenBy<T, K>(
this IOrderedEnumerable<T> source,
Func<T, K> keySelector,
IComparer<K> comparer);
以上两个操作符和之前的操作符类似，就不写例子了。
Reverse
作用：可以输出与输入序列的类型相同，但顺序相反的序列。
原型
public static IEnumerable<T> Reverse<T>(
this IEnumerable<T> source
);
例子
static void Main(string[] args)
{
int[] items = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
var result = items.Reverse();
//显示查询结果
foreach (var item in result)
{
Console.WriteLine(item);
}
Console.Read();
}
结果
