使用GROUP BY和Count（*）将LINQ查询转换为匿名类型 [英] LINQ query with GROUP BY and Count(*) into Anonymous Type

问题描述

我尝试使用LINQ查询来确定每个特定对象类型的数量，并将这些值记录到匿名类型中。

假设我有一些看起来像这样的数据（实际上有暴露这个属性的对象，但它的工作原理是一样的）。

pre $ Group $ $ $ b b 1 b b b 1 b b 2 b b 2 b b 2 b b 3 b b b b b

我知道如何在SQL中格式化查询。它会是这样的：
$ b

SELECT grp = GroupId，cnt = COUNT（*）
FROM myTable
GROUP BY GroupId


在这种情况下，输出可能类似于这个：

  GroupID Count 
 1 2 
 2 3 
 3 1 
  

如何在vb.net中使用LINQ做同样的事情
$ b

  Dim groupCounts =从人在数据
 Group By person.GroupId 
选择新的{group = person.GroupId，count = count（*）} 
  

这并不完全正确，但我认为它很接近。

另外，由于不了解匿名类型，我可以提前宣布 groupCounts 它是一个枚举项，每个项都有一个组a nd count属性？

解决方案

尝试在LinqPad中使用它，并为您的数据库实体创建它应该让您更靠近。

pre $ Public Sub grouper2（）
Dim numbers = New Integer（）{1,1,2,2,2 ，3}

Dim numberGroups =从w在数字中_
Group w By Key = w进入Group _
选择Number = Key，numbersCount = Group.Count（）

'linqpad特定输出
'numberGroups.Dump（）

For Each g In numberGroups
Console.WriteLine（匹配'{0}'的数字' ：，g.Number）
Console.WriteLine（g.numbersCount）
Next

End Sub


I'm trying to use a LINQ query to determine how many of each particular object type I have and record those values into an anonymous type.

Let's say I have some data that looks like this (there are really objects exposing this property, but it'll work the same)

GroupId
1
1
2
2
2
3

I know how to format my query in SQL. It would be something like this:

SELECT grp = GroupId, cnt = COUNT(*)
FROM myTable
GROUP BY GroupId

In this case the output would be something like this:

GroupID  Count
1        2
2        3
3        1

How can I do the same thing with LINQ in vb.net

Dim groupCounts = From person In data
                  Group By person.GroupId
                  Select new {group = person.GroupId, count = count(*)}

That's not quite right, but I think it's close.

Also, not knowing much about anonymous types, can I actually declare groupCounts ahead of time that it will be an enumeration of items which each have a group and count property?

解决方案

Try using this in LinqPad, and subbing out for your database entity it should get you closer.

Public Sub grouper2()
    Dim numbers = New Integer() {1,1,2,2,2,3}

    Dim numberGroups = From w In numbers _
                    Group w By Key = w Into Group _
                    Select Number = Key, numbersCount = Group.Count()

    'linqpad specific output
    'numberGroups.Dump()

    For Each g In numberGroups
        Console.WriteLine("Numbers that match '{0}':", g.Number)
            Console.WriteLine(g.numbersCount)        
    Next

End Sub

这篇关于使用GROUP BY和Count（*）将LINQ查询转换为匿名类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！