如何使用Linq ToDictionary返回字典项中包含多个值的字典？
提问于 2010-01-25 19:15:59
我想将linq查询中的项分组到一个标题下，这样对于每个标题，我都有一个与标题相匹配的对象列表。我假设解决方案是使用ToDictionary来转换对象，但这只允许每个“组”(或字典键)有一个对象。我假设我可以创建类型为(String，List Of())的字典，但我不知道如何编写它。
作为示例，我在下面编写了一个简化版本。
Public Class order
Public ID As Integer
Public Name As String
Public DateStamp As Date
End Class
Public Function GetOrdersSortedByDate() As Generic.Dictionary(Of String, Generic.List(Of User))
Dim orders As New List(Of order)(New order() _
{New order With _
{.ID = 1, .Name = "Marble", .DateStamp = New Date(2010, 1, 1)}, _
New order With _
{.ID = 2, .Name = "Marble", .DateStamp = New Date(2010, 5, 1)}, _
New order With _
{.ID = 3, .Name = "Glass", .DateStamp = New Date(2010, 1, 1)}, _
New order With _
{.ID = 4, .Name = "Granite", .DateStamp = New Date(2010, 1, 1)}})
' Create a Dictionary that contains Package values,
' using TrackingNumber as the key.
Dim dict As Dictionary(Of String, List(Of order)) = _
orders.ToDictionary(Of String, List(Of order))(Function(mykey) mykey.Name, AddressOf ConvertOrderToArray) ' Error on this line
Return dict
End Function
Public Function ConvertOrderToArray(ByVal myVal As order, ByVal myList As Generic.List(Of order)) As Generic.List(Of order)
If myList Is Nothing Then myList = New Generic.List(Of order)
myList.Add(myVal)
Return myList
End Function错误如下
'Public Function ConvertOrderToArray(myVal As order, myList As System.Collections.Generic.List(Of order)) As System.Collections.Generic.List(Of order)'
does not have a signature compatible with delegate
'Delegate Function Func(Of order, System.Collections.Generic.List(Of order))(arg As order) As System.Collections.Generic.List(Of order)'.如何输出每个字典项的列表？
回答 2
Stack Overflow用户
回答已采纳
发布于 2010-01-26 19:48:46
您可以首先按名称对所有结果进行分组，然后使用组密钥作为密钥调用dictionnary
我不知道如何在VB中编写代码，但它在C#中会是什么样子
Dictionary<string,List<Order>> dict = orders
.GroupBy(x => x.Name)
.ToDictionary(gr => gr.Key,gr=>gr.ToList() );Stack Overflow用户
发布于 2010-01-26 22:24:52
您需要的是ToLookup，而不是ToDictionary。查找将存储每个键的值列表，因此键不再需要是唯一的。不过，此方法返回的查找是不可变的。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/2134902
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