Problems with matching duplicates and spotting differences

[XLmuppet]

I hope someone can assist? I have a table with 2500 rows relating to people who have a unique reference number. Some of these users are duplicated by reference number but have other fields in the table (start date in this case) which are not duplicates. I would like to have a formula to group the duplicates together and then mark them (via txt in a new column) if their start dates differ.

i.e in this example

492495​	09/10/2017 15:45​
492495​	26/02/2018 19:12​
492495​	01/03/2018 15:56​
492495​	05/04/2018 15:11​
669250​	09/05/2017 00:57​
669250​	15/04/2020 17:48​
669250​	15/04/2020 17:48​

I would like to indicate that 492495 has all different dates but 669250 has two matching dates.

Any help gratefully received.

 

[GraH]

Hi,
Would this work?

Book1
	A	B	C
1	ref	date	duplicate
2	492495	09/10/2017 15:45	FALSE
3	492495	26/02/2018 19:12	FALSE
4	492495	01/03/2018 15:56	FALSE
5	492495	05/04/2018 15:11	FALSE
6	669250	09/05/2017 00:57	FALSE
7	669250	15/04/2020 17:48	TRUE
8	669250	15/04/2020 17:48	TRUE
Sheet1

Cell Formulas
Range	Formula
C2:C8	C2	=COUNTIFS($A$2:$A$8,A2,$B$2:$B$8,B2)>1

 

[mumps]

VBA approach. Assuming data is in columns A and B, try:

Sub XLmuppet()
    Application.ScreenUpdating = False
    Dim key As Variant, rng As Range, rngList As Object, rngList2 As Object, Val As String
    Cells(1, 1).Sort Key1:=Columns(1), Order1:=xlAscending, Orientation:=xlTopToBottom, Header:=xlYes
    Set rngList = CreateObject("Scripting.Dictionary")
    Set rngList2 = CreateObject("Scripting.Dictionary")
    For Each rng In Range("A2", Range("A" & Rows.Count).End(xlUp))
        If Not rngList.Exists(rng.Value) Then
            rngList.Add rng.Value, Nothing
        End If
    Next
    For Each key In rngList
        With Cells(1, 1)
            .CurrentRegion.AutoFilter 1, key
            For Each rng In Range("B2", Range("B" & Rows.Count).End(xlUp)).SpecialCells(xlCellTypeVisible)
                Val = rng.Value
                If Not rngList2.Exists(Val) Then
                    rngList2.Add key:=Val, Item:=rng.Row
                Else
                    rng.Offset(, 1) = "X"
                    Cells(rngList2(Val), 3) = "X"
                End If
            Next rng
        End With
    Next key
    Range("A1").AutoFilter
    Application.ScreenUpdating = True
End Sub