Delete duplicates from list

[WojTec]

Delphi-Quellcode:

var
  S: string;
  I: Integer;
begin
  for S in List do
  begin
    I := List.IndexOf(S);
    while I = -1 do
    begin
      List.Delete(I);
      I := List.IndexOf(S);
    end;
  end;
end;

...but nothing happen after this. List is TStrings. F1

[Klaus01]

.. could it be that I has never value -1
because S is in the List and you will get for I the position in the List of S.

Delphi-Quellcode:

for S in List do
  begin
    I := List.IndexOf(S);
    while I = -1 do
    begin
      List.Delete(I);
      I := List.IndexOf(S);
    end;
  end;

edit:
If you want to use TStringList there is an property called duplicates
This can be set to avoid duplicate entries in the list.

Best regards
Klaus

[DeddyH]

Delphi-Quellcode:

var
  S: string;
  I, J: Integer;
begin
  for S in List do
  begin
    I := List.IndexOf(S);
    for J := List.Count - 1 downto I + 1 do
      if List[J] = S then
        List.Delete(J);
  end;
end;

Or use a TStringlist as Klaus said before (this TStringlist must have set Sorted to true).

[WojTec]

I found example for TStringList:

Code:

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

but, first is for TStringList - I need for TStrings - it's component property, and second uses sorting and data order is important, so I can't sort it. Thanks for help, guys

[Klaus01]

Delphi-Quellcode:

sList := TStringList.create;
try
  sList.sorted := true;
  sList.duplicates := dupIgnore;
  sList.assign(List);



  List.assign(sList);
finally
  sList.free;
end;

not tested.

Best regards
Klaus

[Bjoerk]

Alternative:

Delphi-Quellcode:

procedure RemoveDoubles(Strings: TStrings);
var
  I, J: integer;
begin
  Strings.BeginUpdate;
  I:= 0;
  while I <= Strings.Count-2 do
  begin
    J:= I+1;
    while J <= Strings.Count-1 do
    begin
      if Strings[I] = Strings[J] then
      begin
        Strings.Delete(J);
        Dec(J);
      end;
      Inc(J);
    end;
    Inc(I);
  end;
  Strings.EndUpdate;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  RemoveDoubles(Memo1.Lines);
end;

[DeddyH]

Da finde ich meinen Vorschlag aber übersichtlicher (nix für ungut).

[Furtbichler]

Schneller (ohne Sort):

Delphi-Quellcode:

For i := List.Count - 1 downto 0 do
  For j := List.Count - 1 downto i + 1 do
    If s[i]=s[j] then 
      s.delete(j);

@DeddyH:  for S in List do I := List.IndexOf(S); entspricht doch For i := 0 to List.Count-1 do S := List[i]; , nur das Letzteres um eine Größenordnung performanter ist oder irre ich mich?

[DeddyH]

Das mag schon sein, ein wenig C&P sei mir doch gegönnt.

[Furtbichler]

Ohne Quellenangabe?