使用 linq 进行高级分组和聚合

Question

我有以下程序：

 void Main()
{



List<Online_video_for_programmers> current_year_videos = new List<Online_video_for_programmers>()
    {
    new Online_video_for_programmers
        {
        video_name="websocket for fortran programmers",
        season=2,
        seasontype=1,
        year=2012
        },
        new Online_video_for_programmers
        {
        video_name="cross site scripting for facebook addicts",
        season=3,
        seasontype=2,
        year=2012
        },

        new Online_video_for_programmers
        {
        video_name="Artificial intelligence for self aware robots",
        season=1,
        seasontype=1,
        year=2012
        }
        ,
        new Online_video_for_programmers
        {
        video_name="Artificial intelligence for self aware robots",
        season=3,
        seasontype=1,
        year=2012
        },

        new Online_video_for_programmers
        {
        video_name="Artificial intelligence for adavanced robots",
        season=5,
        seasontype=1,
        year=2012
        },
    new Online_video_for_programmers
        {
        video_name="Yoga for programmers",
        season=2,
        seasontype=2,
        year=2012
        },
        new Online_video_for_programmers
        {
        video_name="Yoga for programmers",
        season=3,
        seasontype=2,
        year=2012
        }


    };

    //Last years videos sold

List<Online_video_for_programmers> last_year_videos = new List<Online_video_for_programmers>()
    {
    new Online_video_for_programmers
        {
        video_name="websocket for fortran programmers",
        season=2,
        seasontype=1,
        year=2011,
        },
        new Online_video_for_programmers
        {
        video_name="cross site scripting for facebook addicts",
        season=3,
        seasontype=1,
        year=2011,
        },

        new Online_video_for_programmers
        {
        video_name="Artificial intelligence for self aware robots",
        season=2011,
        seasontype=3,
        year=2011,
        }
        ,

    new Online_video_for_programmers
        {
        video_name="Yoga for programmers",
        season=4,
        seasontype=2,
        year=2011,
        },
            new Online_video_for_programmers
        {
        video_name="Yoga for programmers",
        season=2,
        seasontype=2,
        year=2011
        }

};
}
// Define other methods and classes here





 public class Online_video_for_programmers
    {
    public int seasontype {get;set;} //this can be the id of a year, a quater or  month  Tyepes are 1: months, 2, for quarters, 3 for year
public int season {get;set;} //  when season type is 1, season =1 means january. 
    //When season type is 2, season=3 means 3rd quater. When seasontype is 3, season =2011 or 2010 etc... 
        public string video_name {get;set;} //The nambe of the video
        public int year {get;set;} // The year the video was published
}  

我想使用 current_year_videos 和 last_year_videos 来检索去年而不是今年发布的标题。为此，我使用以下代码：

var result=current_year_videos.Concat(last_year_videos).GroupBy( g=> new { seasontype,season,video_name }).Select(s=> new Online_video_for_programmers{  seasontype=s.Key.seasontype, season=s.Key.season, video_name=s.Key.video_name });

上面的代码给了我今年和去年都生产的代码，这样我就可以很容易地找到丢失的代码。

这就是问题所在。 2011年全年制作视频《人工智能自知机器人》，2012年每月制作3期。 我不希望将其视为 2012 年的缺失。只有在 2012 年根本没有产生它时才应该缺失它。问题是，如何调整我的查询以在结果中包含此条件。 到目前为止，我花了一些时间想出不同的东西，但没有成功。

希望有人能提供帮助。

在此先感谢

Answer 1

var result = 
    last_year_videos
       .Select(v => new { v.video_name, v.season })
       .Except(current_year_videos.Select(v => new { v.video_name, v.season }));

给予：

{ video_name = "Artificial intelligence for self aware robots", season = 2011 }
{ video_name = "Yoga for programmers", season = 4 }

更新：如果您想在查看视频时处理季节类型（月、季度、年），那么您可以创建将季节和季节类型转换为月份列表的方法：

private static IEnumerable<int> GetMonths(Online_video_for_programmers video)
{
    switch (video.seasontype)
    {
        case 1: return Enumerable.Range(video.season, 1);
        case 2: return Enumerable.Range((video.season - 1) * 3 + 1, 3);
        case 3: return Enumerable.Range(1, 12);
        default:
            throw new ArgumentException("Unknown season type");
    }
}

使用此方法，您可以检查视频是否与当年的同一视频有几个月的交集：

var currentVideos = 
    current_year_videos.Select(c => new { c.video_name, months = GetMonths(c) });

var result = from v in last_year_videos
             let months = GetMonths(v)
             where !currentVideos.Any(cv => 
                       cv.video_name == v.video_name &&
                       months.Intersect(cv.months).Any())
             select v.video_name;

返回：

"cross site scripting for facebook addicts" // Month 3
"Yoga for programmers" // Months 9,10,11

Answer 2

你想找的：

去年和今年没有出版的书名

但为此，不需要分组：

var result = last_year_videos
    .Where(vLast => !current_year_videos
        .Select(vCurrent => vCurrent.video_name).Contains(vLast.video_name));

您所要做的就是检查带有所选密钥 (video_name) 的视频是否存在于去年的收藏中。