Randomize StringList

by

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:

More Related Contents:

  1. Why cannot take address to a nested local function in 64 bit Delphi?
  2. Delphi: Access Violation at the end of Create() constructor
  3. How to dynamically create controls aligned to the top but after other aligned controls?
  4. How to define application version in one place for multiple applications?
  5. TThreadedQueue not capable of multiple consumers?
  6. Delphi VCL styles tutorial – how to change the style at runtime
  7. Anonymous methods – variable capture versus value capture
  8. How to disable VCL styles in Delphi
  9. Firemonkey Grid Control – Styling a Cell based on a value (via the OnGetValue function call)
  10. How to declare two inter-linked classes?
  11. Why should I not use “if Assigned()” before accessing objects?
  12. Debugging Access Violation errors?
  13. Which variables are initialized when in Delphi?
  14. System Error. Code: 8. Not enough storage is available to process this command
  15. Delphi 2010: How to save a whole record to a file?
  16. Registration-free COM/DLL?
  17. I do not understand what Application.ProcessMessages in Delphi is doing [closed]
  18. How do I let Delphi know I’ve already handled an exception?
  19. How to send a HTTP POST Request in Delphi using WinInet api
  20. How to add mouse wheel support to a component descended from TGraphicControl?
  21. Delphi Conversion Unicode Issues
  22. WWW server reports error after POST Request by Internet Direct components in Delphi
  23. How to add manifest info into delphi project
  24. How to retrieve cpu usage per process
  25. How to detect “dangling pointers” if “Assigned()” can’t do it?
  26. How do I make Beyond Compare ignore certain differences while comparing versions of Delphi Form Files
  27. Delphi 7: ADO, need basic coding example
  28. Looking for a custom image grid
  29. How to translate (internationalize, localize) application?
  30. Using TChromium, Delphi Chromium Embedded

Leave a Comment