출처 : http://delphi.about.com/od/delphitips2009/qt/remove-duplicat.htm

TMemo / TComboBox / TListBox등에서 모두 사용가능한 방법이다.

procedure RemoveDuplicates(const stringList : TStringList) ;
Var
  Buffer : TStringList;
  Cnt    : Integer;
begin
  StringList.Sort;
  Buffer := TStringList.Create;
  Try
    Buffer.Sorted     := True;
    Buffer.Duplicates := dupIgnore;
    Buffer.BeginUpdate;
    For Cnt := 0 To stringList.Count - 1 Do begin
      Buffer.Add(StringList[cnt]) ;
    end;
    Buffer.EndUpdate;
    StringList.Assign(Buffer) ;
  Finally
    FreeandNil(Buffer) ;
  End;
end;

var
  sl : TStringList;
  cnt : integer;
begin
  Randomize;
  sl := TStringList.Create;
  Try
    For cnt := 1 To 100 Do
      sl.Add(IntToStr(Random(100))) ;

    sl.Sorted := True;
    sl.Duplicates := dupIgnore;
    ShowMessage('With duplicates: ' + #13#10 + IntToStr(sl.Count)) ;
    RemoveDuplicates(sl) ;
    ShowMessage('Without duplicates: ' + #13#10 + IntToStr(sl.Count)) ;
  Finally
    sl.Free;
  End;