Ignoring Duplicate entries from drop down list

[Frisbee Dog]

I have a data list where a user can select a value. This list is linked to a separate file which is changed often.

I am using a drop down list box via data validation. Currently, the code I have below works great, as it ignores values that are blank. But, sometimes duplicate entries appear. I would like one of the duplicate to show, but the other to be ignored. I can't figure out how to do this. Please help. Thanks.

=OFFSET(C331,0,0,COUNTIF($C$331:$C$525,">"""),1)

 

[PCL]

Your formula DON'T ignore empty cells when they are inside the list.
A possibility could be to use another list prepared from the first one where all duplicate and empty cells are removed.
Assuming :
data in A2:A8
the second list in D2:D8
Put next formula (coming from someone in this forum) in D2, confirm using CONTROL + SHIFT + ENTER (Area formula)
Copy D2 and drop down

=IF(ROWS(D$2:D2)<=C$2,INDEX(A$2:A$8,SMALL(IF(FREQUENCY(IF(A$2:A$8<>"",MATCH("~"&A$2:A$8,A$2:A$8&"",0)),ROW(A$2:A$8)-ROW(A$2)+1),ROW(A$2:A$8)-ROW(A$2)+1),ROWS(D$2:D2))),"")

 

[PCL]

Or prepare a macro to filter
The first cell where to put filtered data is named = Extract_List
The HEADER where to pick up data is named = Type

Option Explicit
Sub List_Unic_Prepa()
Dim I As Long, J As Long
Dim LASTROW As Long
Dim MyRG As Range
Dim MyCOL As Integer
Dim MyROW As Long
'---------   CLEAR  PREVIOUS  CONTENTS    ----------
    Range(Range("EXTRACT_LIST").Offset(1, 0), Range("EXTRACT_LIST").End(xlDown)).ClearContents
'---------   COLLECT  DATA    ----------
    MyROW = Range("TYPE").Row
    MyCOL = Range("TYPE").Column
    LASTROW = Cells(Rows.Count, MyCOL).End(xlUp).Row
    J = 1
    For I = MyROW + 1 To LASTROW
        Set MyRG = Range(Range("Type"), Cells(I, MyCOL))
        If (WorksheetFunction.CountIf(MyRG, Cells(I, MyCOL)) = 1) Then
            Range("EXTRACT_LIST").Offset(J, 0) = Cells(I, MyCOL)
            J = J + 1
        End If
    Next I
End Sub