procedure TMainForm.RemoveDuplicatesButtonClick(Sender: TObject);
var
  i, j: integer;
  label
    Recheck;
  begin
    Recheck:
    for i := 0 to ListView1.Items.Count - 1 do
      for j := 0 to ListView1.Items.Count - 1 do
        begin
        if i = j then continue;
        if ListView1.Items[i].Caption = ListView1.Items[j].Caption then
          begin
          ListView1.Items.Delete(j);
            goto Recheck;
          end;
          ListView1.Columns[0].Caption := inttostr(ListView1.items.Count);
          end;
          CurrentStatusLabel.caption := 'Removed Duplicates';
    end;

CurrentStatusLabel.caption := 'Removed' + inttostr(j) + 'Duplicates';
 Application.ProcessMessages;  

procedure TMainForm.RemoveDuplicatesButtonClick(Sender: TObject); 
var
  i, j: integer;
  label
    Recheck;
  begin
     Recheck:
    for i := 0 to ListView1.Items.Count - 1 do
       for j := ListView1.Items.Count-1 downto i+1 do
        begin
        if i = j then continue;
        if ListView1.Items[i].Caption = ListView1.Items[j].Caption then
          begin
          ListView1.Items.Delete(j);
            goto Recheck;
          end;
          ListView1.Columns[0].Caption := inttostr(ListView1.items.Count);
          CurrentStatusLabel.caption := 'Removed' + inttostr(j) + 'Duplicates';
          Application.ProcessMessages;
        end;
        //CurrentStatusLabel.caption := 'Removed Duplicates';   // this doesn't give the correct number
    end;

procedure TMainForm.RemoveDuplicatesButtonClick(Sender: TObject); 
  var
    i, j, num_removed: integer;
  begin
    num_removed := 0;
    for i := 0 to ListView1.Items.Count - 1 do
      for j := ListView1.Items.Count-1 downto i+1 do
        begin
        if i = j then continue;  // <-- this line shouldn't be necessary
        if ListView1.Items[i].Caption = ListView1.Items[j].Caption then
          begin
          ListView1.Items.Delete(j);
          inc( num_removed )
          end;
        Application.ProcessMessages;
        end;
    ListView1.Columns[0].Caption := inttostr(ListView1.items.Count);
    CurrentStatusLabel.caption := 'Removed ' + inttostr(num_removed) + ' Duplicates';
  end;

procedure TMaster.DoCleanUp(Sender:TObject);
var i,j,k,ACount:Integer;
    AStrings:TStringList;
    AList:TListItems;
begin
  AList:=lvOne.Items;
  {get a pointer to the listview items. This is faster than attempting
   to dereference using lvOne.Items each time}
  ACount:=AList.Count;//how many items in the list
  AStrings:=TStringList.Create;//create a temporary stringlist
  with AStrings do
  try
    Sorted:=True;
    Duplicates:=dupIgnore;
    //make it a sorted stringlist and ignore duplicates
    for i:=0 to ACount - 1 do AddObject(AList[i].Caption,TObject(i));
    {Add every item in the listview to the stringlist. dupIgnore +
     Sorted ensures that duplicate entries are ignored. We want to
     add entries back to the listview in their original order which
     will not be preserved in the stringlist since it is sorted. So
     we store the original indices in the Objects array of the
     stringlist. Note the TObject(i) typecast.}

    AList.Clear;
    {We have a safe copy of all the listview entries we want to retain so
     why keep the listview entries? Just clear the listview. This issues
     just one LVM_DELETEALLITEMS message as opposed to multiple
     LVM_DELETEITEM messages}
    j:=0;
    {To repopulate the listview we want to start finding its original
     entries starting from the first one, at index 0}
    for i:=0 to ACount - 1 do
    begin
      {The stringlist contains fewer entries than in the original listview
       but nevertheless we have to run this loop as many times as there
       were members in the listview since we need to identify them by
       their original position with the help of the stringlist.Objects
       array}
      k:=IndexOfObject(TObject(j));
      //where is the j'th entry in the listview?
      inc(j);//know that now so next time we want the (j + 1)th entry
      if (k >= 0) then AList.Add.Caption:=Strings[k];
      {The j'th entry could have been a duplicate & may no longer
      exist. Only if it does - add it back to the listview}
    end;
  finally Free end;//don't forget to destroy the stringlist!
  ShowMessage(IntToStr(AList.Count));
end;

procedure TMainForm.RemoveDuplicatesButtonClick(Sender: TObject);
  var
    i, j, num_removed: integer;
    begin
    if ListView1.items.Count > 1000 then  //{after 1,000 lines I thought that the next line would gray out the button.}
    RemoveDuplicatesButton.Enabled := False  //{this line prevents the procedure from continuing but wont gray out until the button is clicked.}
    else
    begin
    num_removed := 0;
    begin
    for i := 0 to ListView1.Items.Count - 1 do
      for j := ListView1.Items.Count-1 downto i+1 do
        begin
        if ListView1.Items[i].Caption = ListView1.Items[j].Caption then
          begin
          ListView1.Items.Delete(j);
          inc( num_removed )
          end;
        Application.ProcessMessages;
        end;
    ListView1.Columns[0].Caption := inttostr(ListView1.items.Count);
    CurrentStatusLabel.caption := 'Removed ' + inttostr(num_removed) + ' Duplicates';
  end;
    end;
    end;