如何根据C#中的值对XML节点进行分组

XDocument doc = XDocument.Load("path/to/xml/file.xml");

<books>
  <book>
    <title>C# in Depth</title>
    <author>Jon Skeet</author>
  </book>
  <book>
    <title>Design Patterns</title>
    <author>Erich Gamma</author>
  </book>
  <book>
    <title>Clean Code</title>
    <author>Robert C. Martin</author>
  </book>
</books>

var groups = from book in doc.Descendants("book")
             group book by (string)book.Element("author") into g
             select new { Author = g.Key, Books = g };

foreach (var group in groups)
{
    Console.WriteLine("Author: " + group.Author);
    
    foreach (var book in group.Books)
    {
        Console.WriteLine("Title: " + book.Element("title").Value);
    }
    
    Console.WriteLine();
}

Author: Jon Skeet
Title: C# in Depth

Author: Erich Gamma
Title: Design Patterns

Author: Robert C. Martin
Title: Clean Code