在一个特定的属性比较两个泛型列表 [英] Comparing two generic lists on a specific property

问题描述

我使用VB.NET使用.NET 2.0。

I'm using VB.NET with .NET 2.0.

我有两个列表，我想在一个特定的属性比较列表中的对象，而不是对象作为一个整体，并创建一个新的列表，其中包含了在一个列表对象，而不是其他。

I have two lists, and I want to compare the lists on a specific property in the object, not the object as a whole, and create a new list that contains objects that are in one list, but not the other.

myList1.Add(New Customer(1,"John","Doe")
myList1.Add(New Customer(2,"Jane","Doe")

myList2.Add(New Customer(1,"","")

在上面的例子中

结果将包含一个客户，李四，因为标识符 2 是不是在第二个列表。

Result in the above example would contain one customer, Jane Doe, because the identifier 2 wasn't in the second list.

您如何比较这两个名单，其中，T＆GT; 或的IEnumerable＆LT; T＆GT; 在.NET 2.0（缺少LINQ）？

How can you compare these two List<T> or any IEnumerable<T> in .NET 2.0 (lacking LINQ)?

推荐答案

下面是C＃版本，VB来了不久......

Here's the C# version, VB coming up shortly...

Dictionary<int, bool> idMap = new Dictionary<int, bool>();
myList2.ForEach(delegate(Customer c) { idMap[c.Id] = true; });

List<Customer> myList3 = myList1.FindAll(
    delegate(Customer c) { return !idMap.ContainsKey(c.Id); });

...这是VB的翻译。需要注意的是VB不具有匿名函数在.NET2，因此，使用的ForEach 和的FindAll 方法会比较笨拙比标准对于每个循环：

...and here's the VB translation. Note that VB doesn't have anonymous functions in .NET2, so using the ForEach and FindAll methods would be more clumsy than standard For Each loops:

Dim c As Customer

Dim idMap As New Dictionary(Of Integer, Boolean)
For Each c In myList2
    idMap.Item(c.Id) = True
Next

Dim myList3 As New List(Of Customer)
For Each c In myList1
    If Not idMap.ContainsKey(c.Id) Then
        myList3.Add(c)
    End If
Next

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