How to loop through two lists simultaneously? - vb.net

Question

I have referred to the following question at: Using foreach loop to iterate through two lists. My question is this, with regards to the chosen answer: Can the o.DoSomething be a comparison? As in:
For Each a in ListA.Concat(ListB)
If(a from ListA=a from ListB) Then
Do Something here
End If
Next
As you might've guessed, I'm using VB.Net and would like to know how I can do what I have shown here. That would basically be to iterate through a joined list separately/independently. Thanks!

Answer 1

Your question indicates that you need a Join operation, because it's not that you want to iterate over two lists, but you also want to match like items from one list to the other.
Dim joinedLists = From item1 In list1 _
Join item2 In list2 _
On item1.Bar Equals item2.Bar _
Select New With {item1, item2}
For Each pair In joinedLists
'Do work on combined item here'
'pair.item1'
'pair.item2'
Next
Other answers recommend Zip. That is simply a function that takes two sequences and produces a single result, much like join, but it is geared to work in a FIFO method over both lists. If you need connections made based on an equality, Join is the specifically built to be right tool for this job.

Answer 2

The answers to my question is-it-possible-to-iterate-over-two-ienumerable-objects-at-the-same-time may help
Dim listA As List(Of A)
Dim listb As List(Of B)
listA.Zip(listb, Function(a, b) a.property1 = b.property1).ForEach(AddressOf Print)
Shared Sub Print(ByVal s As A)
Console.WriteLine(s.Property1)
End Sub

Answer 3

In .Net 4 you could use Zip. Adapted from my answer to this question from a Python fan specifically asking for tuples - you could remove the tuples if you like.
Sub Main()
Dim arr1() As String = {"a", "b", "c"} '' will also work with Lists
Dim arr2() As String = {"1", "2", "3"}
For Each t In TupleSequence(arr1, arr2)
If t.Item1 = t.Item2 Then
'' Do something
End If
Next
Console.ReadLine()
End Sub
Function TupleSequence(Of T1, T2)(
ByVal seq1 As IEnumerable(Of T1),
ByVal seq2 As IEnumerable(Of T2)
) As IEnumerable(Of Tuple(Of T1, T2))
Return Enumerable.Zip(seq1, seq2,
Function(s1, s2) Tuple.Create(s1, s2)
)
End Function

Answer 4

On solution would be to have a dictionary with items from the second list, then loop through your first list and retrieve the corresponding item in the second one, using the dictionary. Here's an example, assuming you want to compare items with an ID property:
Dim DictB = ListB.ToDictionary(Function(x) x.ID)
For each itemA in ListA
If DictB.ContainsKey(itemA.ID)
'Item is in both lists
Dim itemB = DictB(itemA.ID)
'Do something here
End If
Next