How do I get duplicate values from two lists?

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I have a vb program and I would like to use list one values and check for duplicates from 2 lists.
The variable name for the values I am looking for in both lists is strCaseEventInternalID

List one strCaseEventInternalIDList have 3 values 1810458047, 1810458073 and 1810458074.

List two have 3 values 1810458073, 1810458074 and 1810458074
List two is in this object

VB

objXmlResponseDoc2 = Msc.Integration.Mncis.Library.v4.Odyssey.QueryDB(strSql, "Justice", False, True)

There is a duplicate (1810458074) in list two which is what I want to find.
How do I do that?

What I have tried:

VB

For Each strCaseEventInternalID In strCaseEventInternalIDList
    If (strCaseEventInternalIDList.Count() > 1) Then
	'Do something
    End If
Next

Posted 30-Jun-17 3:16am

Member 11403304

Updated 30-Jun-17 9:06am

PIEBALDconsult

v3

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Comments

PIEBALDconsult 30-Jun-17 12:15pm

Put each list in a Hashset and look at the union of them.

3 solutions

Solution 1

Not clear if your question is asking to find duplicate in a list or in between two list. Anyway, here are examples on how to accomplish both scenario

VB

 Dim l1 = New List(Of Integer) From {1810458047, 1810458073, 1810458074}
 Dim l2 = New List(Of Integer) From {1810458073, 1810458074, 1810458074}

'find item that exists in l1 but not l2
 Dim l3 = l1.Except(l2).ToList()  ' result is {1810458047}
 
'find item in both List
 Dim l4 = l1.Intersect(l2).ToList()  ' result is {1810458073,1810458074}

'find duplicate in a List
 Dim duplicates1 = l1.Where(Function(x) l1.Where(Function(y) x = y).Count() > 1).Distinct() 'result is NOTHING
 Dim duplicates2 = l2.Where(Function(x) l2.Where(Function(y) x = y).Count() > 1).Distinct() 'result is 1810458074

 'find duplicates item in l2 that exists in l1
 Dim l5 = l2.Intersect(l1).Where(Function(x) l2.Where(Function(y) x = y).Count() > 1).Distinct().ToList() 'result 1810458074
'find duplicates item in l1 that exists in l2
Dim l6 = l1.Intersect(l1).Where(Function(x) l1.Where(Function(y) x = y).Count() > 1).Distinct().ToList() 'result is NOTHING

.net - how to get duplicate items from a list in vb.net - Stack Overflow[^]

vb.net - Compare two lists and get difference - Stack Overflow[^]

Posted 30-Jun-17 4:25am

Bryian Tan

Updated 30-Jun-17 4:54am

v2

Comments

Member 11403304 30-Jun-17 10:38am

I am trying to find if list two has duplicate values from list one

Bryian Tan 30-Jun-17 10:46am

Then, how about something like

Dim l5 = l2.Intersect(l1).Where(Function(x) l2.Where(Function(y) x = y).Count() > 1).Distinct().ToList()

Member 11403304 30-Jun-17 11:31am

So what do I do with my For each statement? Maybe my question is not clear? List 1 has 3 items and list 2 has 3 items but 2 of the three are duplicates from list one. i.e. 1810458074 from list one appears twice in list two. How do I use a For each and If statements to get that value?

Bryian Tan 30-Jun-17 12:23pm

You can use the for each and linq combination instead of looping through each list. Perhaps I should ask if your application support Linq query, if not then the nested loops from other member should do the work.

Dim l1 = New List(Of Integer) From {1810458047, 1810458073, 1810458074}
        Dim l2 = New List(Of Integer) From {1810458073, 1810458074, 1810458074, 1810458074}

        For Each strCaseEventInternalID In l1
            If l2.FindAll(Function(f As Integer) f = strCaseEventInternalID).Count > 1 Then
                Console.WriteLine(strCaseEventInternalID & " is Duplicate")
            End If
        Next

Solution 3

Quote:
List two have 3 values 1810458073, 1810458074 and 1810458074
There is a duplicate (1810458074) in list two which is what I want to find.

I understand this as searching duplicates in a single list as the list contains 1810458074 2 times.

VB

Dim list1 = New List(Of Integer) From {1810458073, 1810458074, 1810458074}
For x = LBound(list1) to UBound(list1) - 1
  For y = x + 1 to UBound(list1)
    If list1(x) = list1(x) then
      ' found duplicate
    End If
  Next
Next

Posted 30-Jun-17 9:06am

Patrice T

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User 7407470 · Accepted Answer · 2017-06-30T06:05:00

Solution 2

If you want to use 'For Each' (and don't care if there are duplicates in list1 or list2 itself):

VB

For Each val1 As Integer In list1
    For Each val2 As Integer In list2
        If val1 = val2 Then
        ' found duplicate
        End If
    Next
Next

(Edit: added 'Then' with 'If')

Posted 30-Jun-17 6:05am

User 7407470

Updated 30-Jun-17 6:47am

v2

Comments

Member 11403304 30-Jun-17 13:10pm

Thank you so much Peter. Your code with some tweaking is working. You made my day!

[no name] 30-Jun-17 13:16pm

You're welcome. Glad you liked it!