Question

我有一个DataTable，它有这个结构和数据：

id |   inst   |   name
------------------------
 1 |  guitar  |  john
 2 |  guitar  |  george
 3 |  guitar  |  paul
 4 |  drums   |  ringo
 5 |  drums   |  pete

我可以检索这样的记录：

IEnumerable <Beatle>...

class Beatle
{
  int id;
  string inst;
  string name;
}

我想得到那些演奏不同乐器的人的内部秩序。在MSSQL中我会使用

SELECT 
    *
    ,Row_Number() OVER (PARTITION BY inst ORDER BY id) AS rn
FROM Beatles

此查询返回

id |   inst   |   name  | rn
-----------------------------
 1 |  guitar  |  john   | 1
 2 |  guitar  |  george | 2
 3 |  guitar  |  paul   | 3
 4 |  drums   |  ringo  | 1
 5 |  drums   |  pete   | 2

我如何在 Linq ？

中执行此操作

编辑。（接受回答后）

完整的工作代码：

var beatles = (new[] { new { id=1 , inst = "guitar" , name="john" },
    new { id=2 , inst = "guitar" , name="george" },
    new { id=3 , inst = "guitar" , name="paul" },
    new { id=4 , inst = "drums" , name="ringo" },
    new { id=5 , inst = "drums" , name="pete" }
});

var o = beatles.OrderBy(x => x.id).GroupBy(x => x.inst)
               .Select(g => new { g, count = g.Count() })
               .SelectMany(t => t.g.Select(b => b)
                                   .Zip(Enumerable.Range(1, t.count), (j, i) => new { j.inst, j.name, rn = i }));

foreach (var i in o)
{
    Console.WriteLine("{0} {1} {2}", i.inst, i.name, i.rn);
}

Answer 1

试试这个衬垫：

var o = beatles
    .OrderBy( x => x.id )
    .GroupBy( x => x.inst )
    .Select( group => new { Group = group, Count = group.Count() } )
    .SelectMany( groupWithCount =>
        groupWithCount.Group.Select( b => b)
        .Zip(
            Enumerable.Range( 1, groupWithCount.Count ),
            ( j, i ) => new { j.inst, j.name, RowNumber = i }
        )
    );

foreach (var i in o)
{
    Console.WriteLine( "{0} {1} {2}", i.inst, i.name, i.RowNumber );
}

输出：

Guitar John 1
Guitar George 2
Guitar Paul 3
drums Ringo 1
drums Pete 2

Answer 2

B＆＃34; H

我知道这是旧的。但为什么简单的解决方案呢？

var o = beatles.GroupBy(x => x.inst)
               .SelectMany(g =>
                   g.Select((j, i) => new { j.inst, j.name, rn = i + 1 })
               );

Answer 3

另一个想法是使用视图，如果可能的话。

Answer 4

正如@The_Smallest指出的那样，LINQ不支持行号。以下是您可以获得所需内容的方法：

var grouped = beatles.OrderBy( x => x.id )
  .ToList()   // required because SelectMany below doesn't evaluate to SQL
  .GroupBy( x => x.inst );
var rns = grouped.ToDictionary( x => x.Key, x => 1 );
var result = grouped
  .SelectMany( x => x.Select( 
    y => new { inst = y.inst, name = y.name, rn = rns[y.inst]++ } ) );

Answer 5

有些人可能会在您的代码中找到有用的方法来获取正确的索引

.Select((item, i) => new { Item = item, Index = i })

Answer 6

另一种解决方法，相当于RANK（）OVER（PARTITION BY“partitionBy”ORDER BY“orderBy”DESC）：

 DataTable Rank(DataTable dt, string partitionBy, string orderBy, int whichRank)
   {

        DataView dv = new DataView(dt);
        dv.Sort = partitionBy + ", " + orderBy + " DESC";

        DataTable rankDt = dv.ToTable();
        rankDt.Columns.Add("Rank");
        int rank = 1;

        for (int i = 0; i < rankDt.Rows.Count - 1; i++)
        {
            rankDt.Rows[i]["Rank"] = rank;
            DataRow thisRow = rankDt.Rows[i];
            DataRow nextRow = rankDt.Rows[i + 1];

            if (thisRow[partitionBy].ToString() != nextRow[partitionBy].ToString())
                rank = 1;
            else
                rank++;
        }

        DataView selectRankdv = new DataView(rankDt);
        selectRankdv.RowFilter = "rank = " + whichRank;
        return selectRankdv.ToTable();
  }

Answer 7

https://github.com/jurioli/Applied

var result = data.GroupBy(a => new { a.inst }).AsPartition()
.Over(p => p.RowNumber(), (a, value) => new { a.inst, a.name, RowNumber = value })
.ToList();

Linq中的Row_number（分区xxx）？

7 个答案: