linq计数二次分组和计数不分组

Question

我正在尝试构建一个用于统计的摘要查询。

我有一个包含以下列的数据表（大约 18000 行）：

Artist / Album / file_path (one for each song) / rating / 

每个艺术家有 1 个或多个专辑，其中包含歌曲，每首歌曲都有评分

我想得到以下结果：

对于每个艺人ID（比艺人名更可靠），专辑总数、歌曲总数、评分总数等于5。

Artist x / #album / #songs / #rating = 5 / song.first() //in song.first i have access to the file path, it can be any file path from the artist hence the first one.

我已经拉了几个小时的头发，但我无法获得每位艺术家的专辑数量：（这是我迄今为止一直在尝试的：

我有一个查询类：

  public class art_detail
    {
        public string artiste { get; set; }
        public string fp { get; set; } // the file_path
        public int nbr_album { get; set; }
        public int nbr_song { get; set; }
        public int nbr_rat5 { get; set; }
    }

这是我提出的查询：

            var result = from res in Globals.ds.Tables[0].AsEnumerable() // the table
           .GroupBy(x =>  new { art = x.Field<int>("Artist_ID"), alb = x.Field<string>("album") })
           .Select(x => new art_detail { artiste = x.Select(p =>p.Field<string>("artiste")).First(), fp = x.Select(p=>p.Field<string>("file_path")).First(), nbr_album = x.Key.alb.Count() })
           .OrderBy(x => x.artiste)
                  select res;

不幸的是，计数完全错误，我不知道如何获得评分 = 5 :(

感谢您的帮助！

编辑： 这是我让它工作的查询：

               var table = Globals.ds.Tables[0].AsEnumerable();
               var stats = table.GroupBy(x => x.Field<int>("Artist_ID"))
                .Select(x => new art_detail
                {
                     artiste = x.Select(p=>p.Field<string>("artiste")).First(),
                     nbr_album = x.Select(y => y.Field<string>("album")).Distinct().Count(),
                     fp = x.Select(y => y.Field<string>("file_path")).FirstOrDefault(),
                     nbr_song = x.Count(),
                     nbr_rat5 = x.Count(y => y.Field<int>("Rating") == 5)
                 });

比我想象的要简单:)

Answer 1

假设一个表的模式与这个类匹配：

public class Song
{
    public string ArtistID { get; set; }
    public string Album { get; set; }
    public string FilePath { get; set; }
    public int Rating { get; set; }
}

给定一个 LINQ 源，您有以下查询：

IQueryable<Song> table = /*insert source*/;
var stats = table.GroupBy(x => x.ArtistID);
                 .Select(x => new art_detail
                 {
                     artiste = x.Key,
                     nbr_album = x.Select(y => y.Album).Distinct().Count(),
                     nbr_song = x.Count(),
                     nbr_rat5 = x.Count(y => y.Rating == 5),
                 });

Answer 2

我使用了头部编译查询，因为在这种情况下它对我来说似乎更容易理解：

示例模型：

public class Artist
{
    public string ArtistID { get; set; }
    public string Album { get; set; }
    public string FilePath { get; set; }
    public int Rating { get; set; }
    public int NumberOfSongs { get; set; }
}

为 Usher 和 Beyonce 创建一些虚拟记录：

//Usher
var artistOne = new Artist() 
{
    ArtistID = "Usher",
    Album = "Lit",
    FilePath = "dummy/path/here",
    Rating = 5,
    NumberOfSongs = 9
};
var artistTwo = new Artist() 
{
    ArtistID = "Usher",
    Album = "Sick",
    FilePath = "dummy/path/here",
    Rating = 5,
    NumberOfSongs = 11
};
var artistThree = new Artist() 
{
    ArtistID = "Usher",
    Album = "Dope",
    FilePath = "dummy/path/here",
    Rating = 4,
    NumberOfSongs = 14
};

//Beyonce
var artistFour = new Artist() 
{
    ArtistID = "Beyonce",
    Album = "Hot",
    FilePath = "dummy/path/here",
    Rating = 5,
    NumberOfSongs = 8
};
var artistFive = new Artist() 
{
    ArtistID = "Beyonce",
    Album = "Fire",
    FilePath = "dummy/path/here",
    Rating = 4,
    NumberOfSongs = 16
};

var listOfArtist = new List<Artist> { artistOne, artistTwo, artistThree, artistFour, artistFive };

运行查询：

var result =  from a in listOfArtist
              where a.Rating == 5
              group a by a.ArtistID into art
              select new
              {
                 artist = art.Key,
                 numberOfAlbums = art.Count(),
                 numberOfSongs = art.Sum(d => d.NumberOfSongs),
              }; 

结果：

希望这会有所帮助 =)