Excel /有效地识别（准确）字符串在特定表列（35K行）中的出现

Question

I've a table with 35000 rows, each row should have a unique (alphanumeric) ID, but I need to check this. Using countif takes an age to calculate, what would be the most efficient (least calculation time).

[ID] | [Occurences]
[A7A8S8D9] | [<formula>]
[F6F7F8F9] | [<formula>]

Answer 1

If you don't mind a VBA solution this will place 'Duplicate' next to all duplicate ID's except the first.

I tested it on 35,000 numeric ID's created using =RANDBETWEEN(1, 1000) and it ran in 671ms. It may run faster if you pass the range into an array.

'Remove line to remove timing.
Private Declare Function GetTickCount Lib "kernel32" () As Long

'Will not mark first occurrence as duplicate.
Public Sub CheckForDuplicates()

    Dim rng As Range
    Dim rCell As Range
    Dim dict As Object

    'Remove next two lines to remove timing.
    Dim TC As Long
    TC = GetTickCount

    'Update sheet name as required.
    With ThisWorkbook.Worksheets("Sheet1")
        'Defines range as A2 to last row containing data (providing there's no empty cells in col A).
        '-1 at end of line as we're starting on row 2.
        Set rng = .Range("A2").Resize(.Cells(Rows.Count, 1).End(xlUp).Row - 1)
    End With
    Set dict = CreateObject("Scripting.Dictionary")

    With dict
        For Each rCell In rng
            If .Exists(rCell.Value) Then
                rCell.Offset(, 1) = "Duplicate"
            Else
               .Add rCell.Value, rCell.Value
            End If
        Next rCell
    End With

    'Remove line to remove timing.
    MsgBox GetTickCount - TC & "ms elapsed."

End Sub