LINQ VB如何检查对象列表中的重复项

Question

我有一个对象列表，每个对象都有2个相关属性：“ ID”和“ Name”。让我们将列表称为“ lstOutcomes”。我需要检查列表中是否存在重复项（意思是object1.ID = object2.ID等），如果至少有一个重复项，请设置一个标志（valid = false或其他内容）。同样，当对象失败时，向用户发送一条消息，提及对象的“名称”，将是很好的选择。

我确定我将需要使用Group By运算符来执行此操作，但是我不习惯在LINQ中执行此操作，并且那里的示例对我没有帮助。 This article似乎与我需要的接近，但不完全相同，它在C＃中。

这里是一个开始的刺...

Dim duplist = _
    (From o As objectType In lstOutcomes _
    Group o By o.ID Into g = Group _
    Let dups = g.Where(Function(h) g.Count > 1) _
    Order By dups Descending).ToArray

if duplist.count > 0 then
valid = false
end if

帮助？

Answer 1

我将用C＃编写它，但希望您可以将其转换为VB。它不使用join且为O（n log n），我假设您有List<T>：

lst.Sort();  //O(nlogn) part.

var duplicatedItems = lst.Skip(1).Where((x,index)=>x.ID == lst[index].ID);

Answer 2

Dim itemsGroupedByID = lstOutcomes.GroupBy(Function(x) x.ID)
Dim duplicateItems = itemsGroupedByID.Where(Function(x) x.Count > 1) _
                                     .SelectMany(Function(x) x) _
                                     .ToList()

If duplicateItems.Count > 0
    valid = False
    Dim errorMessage = "The following items have a duplicate ID: " & _
                       String.Join(", ", duplicateItems.Select(Function(x) x.Name))
End If

Answer 3

我将收回Saeed Amiri在C＃中所说的话，并完成它。

        lst.Sort()
        Dim valid As Boolean = true
    dim duplicatedItems = lst.Skip(1) _
        .Where(Function(x,index) x.ID = lst(index).ID)

    Dim count As Integer = duplicatedItems.Count()
    For Each item As objectType In duplicatedItems
        valid = False
        Console.WriteLine("id: " & item.ID & "Name: " & item.Name)
    Next

Answer 4

该项目在后面，我只是这样将其砍死：

    ' For each outcome, if it is in the list of valid outcomes more than once, and it is not in the list of 
    ' duplicates, add it to the duplicates list.
    Dim lstDuplicates As New List(Of objectType)
    For Each outcome As objectType In lstOutcomes
        'declare a stable outcome variable
        Dim loutcome As objectType = outcome
        If lstOutcomes.Where(Function(o) o.ID = loutcome.ID).Count > 1 _
        AndAlso Not lstDuplicates.Where(Function(d) d.ID = loutcome.ID).Count > 0 Then
            lstDuplicates.Add(outcome)
        End If
    Next
    If lstDuplicates.Count > 0 Then
        valid = False
        sbErrors.Append("There cannot be multiple outcomes of any kind. The following " & lstDuplicates.Count & _
                        " outcomes are duplicates: ")
        For Each dup As objectType In lstDuplicates
            sbErrors.Append("""" & dup.Name & """" & " ")
        Next
        sbErrors.Append("." & vbNewLine)
    End If

Answer 5

已经晚了，虽然可以帮助别人。

您可以使用一对非常干净的单线实现此目的：

Dim lstOutcomes As IList(Of T)

Dim FoundDuplicates As Boolean
FoundDuplicates = lstOutcomes.Any(Function(p) lstOutcomes.ToArray.Count(Function(q) p.ID = q.ID and p.Name=q.Name) > 1)

Dim ListOfDuplicates As IList(Of T)
ListOfDuplicates = lstOutcomes.Where(Function(p) lstOutcomes.ToArray.Count(Function(q) p.ID = q.ID And p.Name = q.Name) > 1)

然后您可以清除重复列表，使其仅包含一次重复：

Dim CleanList as IList(of T)
For Each MyDuplicate As T in ListOfDuplicates
    If not CleanList.Any(function(p) p.ID = MyDuplicate.ID And p.Name = MyDuplicate.Name) then
        CleanList.Add(MyDuplicate)
    End If
Next

或者作为单行，尽管阅读效果不佳

ListOfDuplicates.ForEach(sub(p) If not CleanList.Any(function(q) p.ID = q.ID And p.Name = q.Name) then CleanList.Add(p))

最后，作为对将来要求的预期，应该将“重复项是什么”定义为单独的内容。委托对此非常方便：

Dim AreDuplicates as Func(of T, T, Boolean) = Function(a,b) a.ID = b.ID And a.Name = b.Name
FoundDuplicates = lstOutcomes.Any(Function(p) lstOutcomes.ToArray.Count(Function(q) AreDuplicates(p,q) ) > 1)