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Remove Duplicate Items in Delphis TStringList
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Title: Remove Duplicate Items in Delphi's TStringList
Tip submitted by Jens Borrisholt
The non-visual component Delphi class, TStringList, stores and manipulates a list of strings. Each string can be associates with an object.
The TStringList is derived from the base class for storing strings, TStrings.
Many Delphi controls like TListBox, TComboBox and TMemo, for example, expose a property which is of the TStrings type: Items for TListBox, Lines for TMemo.
Removing Duplicates from a TStringList
When you fill in a string list with string items you might end up with a list holding duplicate strings - more than one item with the "same" string value.
To remove duplicate values from the string list use the following procedure:
//remove duplicate strings from the string list
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
buffer.Add(stringList[cnt]) ;
buffer.EndUpdate;
stringList.Assign(buffer) ;
finally
FreeandNil(buffer) ;
end;
end;
Here's an example of usage:
var
sl : TStringList;
cnt : integer;
begin
Randomize;
sl := TStringList.Create;
try
for cnt := 1 to 1000 do
sl.Add(IntToStr(Random(2000))) ;
ShowMessage('With duplicates: ' + #13#10 + IntToStr(sl.Count)) ;
RemoveDuplicates(sl) ;
ShowMessage('Without duplicates: ' + #13#10 + IntToStr(sl.Count)) ;
finally
sl.Free;
end;
end;
Note: Randomize initializes the random number generator; Random returns a randomly generated number within a specified range.
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