如何：按任意词或字段对文本数据进行排序或筛选 (LINQ)
下面的示例演示如何按结构化文本（如逗号分隔值）行中的任意字段对该文本行进行排序。 可在运行时动态指定该字段。 假定 scores.csv 中的字段表示学生的 ID 号，后面跟四个测验分数。
创建一个包含数据的文件
- 从主题如何：联接不同文件的内容 (LINQ) 中复制 scores.csv 数据并将其保存到解决方案文件夹中。
示例
Class SortLines
Shared Sub Main()
Dim scores As String() = System.IO.File.ReadAllLines("../../../scores.csv")
' Change this to any value from 0 to 4
Dim sortField As Integer = 1
Console.WriteLine("Sorted highest to lowest by field " & sortField)
' Demonstrates how to return query from a method.
' The query is executed here.
For Each str As String In SortQuery(scores, sortField)
Console.WriteLine(str)
Next
' Keep console window open in debug mode.
Console.WriteLine("Press any key to exit.")
Console.ReadKey()
End Sub
Shared Function SortQuery(
ByVal source As IEnumerable(Of String),
ByVal num As Integer) As IEnumerable(Of String)
Dim scoreQuery = From line In source
Let fields = line.Split(New Char() {","})
Order By fields(num) Descending
Select line
Return scoreQuery
End Function
End Class
' Output:
' Sorted highest to lowest by field 1
' 116, 99, 86, 90, 94
' 120, 99, 82, 81, 79
' 111, 97, 92, 81, 60
' 114, 97, 89, 85, 82
' 121, 96, 85, 91, 60
' 122, 94, 92, 91, 91
' 117, 93, 92, 80, 87
' 118, 92, 90, 83, 78
' 113, 88, 94, 65, 91
' 112, 75, 84, 91, 39
' 119, 68, 79, 88, 92
' 115, 35, 72, 91, 70
public class SortLines
{
static void Main()
{
// Create an IEnumerable data source
string[] scores = System.IO.File.ReadAllLines(@"../../../scores.csv");
// Change this to any value from 0 to 4.
int sortField = 1;
Console.WriteLine("Sorted highest to lowest by field [{0}]:", sortField);
// Demonstrates how to return query from a method.
// The query is executed here.
foreach (string str in RunQuery(scores, sortField))
{
Console.WriteLine(str);
}
// Keep the console window open in debug mode.
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
// Returns the query variable, not query results!
static IEnumerable<string> RunQuery(IEnumerable<string> source, int num)
{
// Split the string and sort on field[num]
var scoreQuery = from line in source
let fields = line.Split(',')
orderby fields[num] descending
select line;
return scoreQuery;
}
}
/* Output (if sortField == 1):
Sorted highest to lowest by field [1]:
116, 99, 86, 90, 94
120, 99, 82, 81, 79
111, 97, 92, 81, 60
114, 97, 89, 85, 82
121, 96, 85, 91, 60
122, 94, 92, 91, 91
117, 93, 92, 80, 87
118, 92, 90, 83, 78
113, 88, 94, 65, 91
112, 75, 84, 91, 39
119, 68, 79, 88, 92
115, 35, 72, 91, 70
*/
此示例还演示如何从函数 (Visual Basic) 或方法 (C#) 返回查询变量。
编译代码
创建一个面向 .NET Framework 3.5 版的 Visual Studio 项目。 默认情况下，该项目具有对 System.Core.dll 的引用以及针对 System.Linq 命名空间的 using 指令 (C#) 或 Imports 语句 (Visual Basic)。 在 C# 项目中，添加 System.IO 命名空间的 using 指令。
将此代码复制到您的项目。
按 F5 编译并运行程序。
按任意键退出控制台窗口。