Highlight duplicates across a workbook

Question

I am trying to highlight duplicates across a workbook of 12 sheets.

We track ID#s and I want to highlight the cell if an ID# (value) is on any of the other sheets.

Answer 1

Here is a simplified example that should give you some ideas and point you in the right direction. If you have an questions, let me know.

Sub collected_ids_example()
    ' enable microsoft scripting runtime --> tools - references
    ' For convenience I put all code in 2 subs/functions
    ' This code assumes you want every cell with a duplicate id highlighted.
    ' Although it is easy enough to modify that if you want.

    Dim sh As Worksheet
    Dim id_to_addresses As New Dictionary
    Dim id_ As Range

    ' For every worksheet collect all ids and their associated adressses
    ' for the specified range.
    For Each sh In ThisWorkbook.Sheets
        For Each id_ In sh.Range("A4:A100")
            If Not IsEmpty(id_) Then
                If Not id_to_addresses.Exists(id_.Value) Then
                    Set id_to_addresses(id_.Value) = New Collection
                End If
                id_to_addresses(id_.Value).Add get_full_address(id_)
            End If
        Next id_
    Next sh

    ' Color each cell with a duplicate id
    Dim collected_id As Variant
    Dim adresses As Collection
    Dim c As Range
    For Each collected_id In id_to_addresses
        Dim duplicate_address As Variant
        Set adresses = id_to_addresses(collected_id)

        'You have a duplicate if an id is associated with more than 1 addrress
        If adresses.Count >= 2 Then
            For Each duplicate_address In adresses
                Set c = Range(duplicate_address)
                c.Interior.ColorIndex = 3
            Next duplicate_address
        End If
    Next collected_id
End Sub

Private Function get_full_address(c As Range) As String
    get_full_address = "'" & c.Parent.Name & "'!" & c.Address(External:=False)
End Function