Sort part of a list in descending order (by date), the other part in ascending order (alphabetically)?

Question

I have a control which shows a list of all PDFs in a selected folder. The names of most of these PDFs (for example, meeting minutes) begin with a date. I want these PDFs shown in descending order so that the most recent PDFs are shown at the top.

In the same folder I also have some PDFs whose names do not contain a date (for example, policies). I want these files to be ordered alphabetically.

Here is an example of the kind of list I have and how I want it to be ordered:

• 2019-01-12 Meeting minutes.pdf
• 2018-11-19会议议程.pdf
• 2018-06-02会议记录.pdf
• 2017-12-13会议议程.pdf
• 2017-04-27会议纪要.pdf
• 隐私政策.pdf
• 保障政策.pdf
• 福利政策.pdf

这是我尝试过的：

private void GenerateFolder()
{
    folder_path = Server.MapPath(BaseFolder);
    _folder_view = new StringBuilder();

    if (Directory.Exists(folder_path))
    {
        DirectoryInfo info = new DirectoryInfo(folder_path);
        FileInfo[] files = info.GetFiles().OrderByDescending(p => p.FullName).ToArray();

        foreach (FileInfo file in files)
        { 
            doStuff();
        }
    }

    folder_view.Text = _folder_view.ToString();
}

使用此代码，名称以日期开头的PDF按我想要的降序排列（按日期）。但是其他名称不是以日期开头的PDF 却没有按照我想要的方式（按字母顺序）排序。有没有办法实现我的双重分类目标？

Answer 1

我将创建一个自定义类，将日期和文件名的其余部分解析为单独的属性，然后您可以使用OrderByDescending和ThenBy对这些单独的属性进行排序。

public class ParsedFilename
{
    public ParsedFilename(string filename)
    {
        FullName = filename;
        if (filename.Length >= 12 &&
            DateTime.TryParse(filename.Substring(0, 10), out var date))
        {
            Date = date;
            Name = filename.Substring(11);
        }
        else
        {
            Date = null;
            Name = filename;
        }
    }

    public DateTime? Date { get; }
    public string Name { get; }
    public string FullName { get; }
}

你可以这样使用它：

var data = new List<string>(new[]
    {
        "2019-01-12 Meeting minutes.pdf",
        "Safeguarding policy.pdf",
        "2017-04-27 Meeting minutes.pdf",
        "2018-06-02 Meeting minutes.pdf",
        "2017-12-13 Meeting agenda.pdf",
        "Privacy policy.pdf",
        "Welfare policy.pdf",
        "2018-11-19 Meeting agenda.pdf"
    });

var parsedData = data.Select(d => new ParsedFilename(d));

var sortedData = parsedData.OrderByDescending(d => d.Date)
                           .ThenBy(d => d.Name);

var output = sortedData.Select(d => d.FullName);

它产生以下输出：

2019-01-12 会议纪要.pdf
2018-11-19 会议议程.pdf
2018-06-02 会议纪要.pdf
2017-12-13 会议议程.pdf
2017-04-27 会议纪要.pdf
隐私政策
.pdf政策.pdf
福利政策.pdf

根据目录中文件名的格式，您可能需要添加一些更强大的解析。