delphi - Randomize StringList

Question

How can I randomize the Strings in the StringList similarly how this online tool works. If anyone is familiar with it, check this: http://textmechanic.co/Randomize-List.html

Answer 1

One common algorithm to perform a shuffle is the Fisher-Yates shuffle. This generates uniformly distributed permutations.

To implement on a Delphi TStrings object you can use this:

procedure Shuffle(Strings: TStrings);
var
  i: Integer;
begin
  for i := Strings.Count-1 downto 1 do 
    Strings.Exchange(i, Random(i+1));
end;

Now, whilst in theory this will generate uniformly distributed permutations, the actual performance depends heavily on the quality of the random number generator. This is discussed in Knuth's Art of Computer Programming, volume 2, section 3.4.2, Algorithm P.

Further reading:

• Fisher-Yates shuffle (Wikipedia)
• Jeff Attwood's two blog articles on shuffling: Shuffling and The Danger of Na?veté
• The intuition behind Fisher-Yates shuffling (Eli Bendersky)
• Art of Computer Programming, Donald Knuth, volume 2, section 3.4.2
• Shuffling (Wikipedia)