Question

我的预期输出是：

扩展名：.txt-CATS.TXT-DOGS.TXT扩展名：.pdf- INFO.PDF-TEST2.PDF扩展名：.doc-Summary.DOC- TEST1.DOC

这里是功能。

    public void TestGroupByFluentSyntax()
    {
        string[] files = new string[] { "test1.doc", "test2.pdf", "cats.txt", "dogs.txt", "info.pdf", "summary.doc" };

        IEnumerable<IGrouping<string, string>> query = files.GroupBy(file => System.IO.Path.GetExtension(file), file => file.ToUpper())
                                                            .OrderBy(grouping => grouping.Key);

        foreach(IGrouping<string, string> grouping in query)
        {
            Console.WriteLine("Extension: " + grouping.Key);
            foreach (string fileName in grouping)
                Console.WriteLine("   -- " + fileName);
        }
    }

    public void TestGroupByFluentSyntax2()
    {
        string[] files = new string[] { "test1.doc", "test2.pdf", "cats.txt", "dogs.txt", "info.pdf", "summary.doc" };

        IEnumerable<IGrouping<string, string>> query = files.OrderBy(file => file).GroupBy(file => System.IO.Path.GetExtension(file), file => file.ToUpper());

        foreach (IGrouping<string, string> grouping in query)
        {
            Console.WriteLine("Extension: " + grouping.Key);
            foreach (string fileName in grouping)
                Console.WriteLine("   -- " + fileName);
        }
    }

如果我先订购，然后将其分组。但是分组和排序却没有。我在分组并排序后的功能 TestGroupByFluentSyntax （）'上缺少什么？

Answer 1

您并不遥远。在TestGroupByFluentSyntax()中，您的输出为：

Extension: .doc
   -- TEST1.DOC
   -- SUMMARY.DOC
Extension: .pdf
   -- TEST2.PDF
   -- INFO.PDF
Extension: .txt
   -- CATS.TXT
   -- DOGS.TXT

您按扩展名分组并按扩展名排序。因此，显示时，扩展名来自doc，pdf和txt。但是每个组中的文件未排序。您可以实现所需的输出（通过反转扩展顺序-将OrderByDescending用作：

IEnumerable<IGrouping<string, string>> query 
    = files.GroupBy(file => System.IO.Path.GetExtension(file), file => file.ToUpper())
                   .OrderByDescending(grouping => grouping.Key);

然后，当您显示（对每个组进行排序-使用OrderBy）时，请使用：

foreach (string fileName in grouping.OrderBy(name => name))
    Console.WriteLine("  -- " + fileName);

这将是输出：

Extension: .txt
   -- CATS.TXT
   -- DOGS.TXT
Extension: .pdf
   -- INFO.PDF
   -- TEST2.PDF
Extension: .doc
   -- SUMMARY.DOC
   -- TEST1.DOC

Answer 2

    This worked:

    public void TestGroupByFluentSyntax()
    {
        Console.WriteLine("TestGroupByFluentSyntax");

        string[] files = new string[] { "test1.doc", "test2.pdf", "cats.txt", "dogs.txt", "info.pdf", "summary.doc" };

        IEnumerable<IGrouping<string, string>> query = files.GroupBy(file => System.IO.Path.GetExtension(file), file => file.ToUpper());

        foreach (IGrouping<string, string> grouping in query)
        {
            Console.WriteLine("Extension: " + grouping.Key);

            foreach (string fileName in grouping.OrderBy(name => name))
                Console.WriteLine("   -- " + fileName);
        }
    }

LINQ分组和排序无法按预期进行

2 个答案: