用linq实现密集排名

使用以下linq代码，如何在我的结果中添加dense_rank？ 如果这太慢或太复杂，那么只有排名窗口function怎么样？

var x = tableQueryable .Where(where condition) .GroupBy(cust=> new { fieldOne = cust.fieldOne ?? string.Empty, fieldTwo = cust.fieldTwo ?? string.Empty}) .Where(g=>g.Count()>1) .ToList() .SelectMany(g => g.Select(cust => new { cust.fieldOne , cust.fieldTwo , cust.fieldThree })); 

Answer 1

这是一个dense_rank() 。 根据您的需要更改GroupBy和Order :)基本上， dense_rank正在对查询的有序组进行编号，因此：

 var DenseRanked = data.Where(item => item.Field2 == 1) //Grouping the data by the wanted key .GroupBy(item => new { item.Field1, item.Field3, item.Field4 }) .Where(@group => @group.Any()) // Now that I have the groups I decide how to arrange the order of the groups .OrderBy(@group => @group.Key.Field1 ?? string.Empty) .ThenBy(@group => @group.Key.Field3 ?? string.Empty) .ThenBy(@group => @group.Key.Field4 ?? string.Empty) // Because linq to entities does not support the following select overloads I'll cast it to an IEnumerable - notice that any data that i don't want was already filtered out before .AsEnumerable() // Using this overload of the select I have an index input parameter. Because my scope of work is the groups then it is the ranking of the group. The index starts from 0 so I do the ++ first. .Select((@group , i) => new { Items = @group, Rank = ++i }) // I'm seeking the individual items and not the groups so I use select many to retrieve them. This overload gives me both the item and the groups - so I can get the Rank field created above .SelectMany(v => v.Items, (s, i) => new { Item = i, DenseRank = s.Rank }).ToList(); 

另一种方式是Manoj在这个问题中的答案所指定的 – 但我更喜欢它，因为从表中选择了两次。

Answer 2

因此，如果我理解正确，那么密集等级是订购组时的组的索引。

 var query = db.SomeTable .GroupBy(x => new { x.Your, x.Key }) .OrderBy(g => g.Key.Your).ThenBy(g => g.Key.Key) .AsEnumerable() .Select((g, i) => new { g, i }) .SelectMany(x => xgSelect(y => new { y.Your, y.Columns, y.And, y.Key, DenseRank = xi, } );