Programming Praxis

14 Responses to “Fortune”

1. Programming Praxis – Fortune « Bonsai Code said

   April 5, 2011 at 9:35 AM

   […] today’s Programming Praxis exercise, our goal is to implement the fortune Unix command line tool. […]
2. Remco Niemeijer said

   April 5, 2011 at 9:35 AM

   My Haskell solution (see http://bonsaicode.wordpress.com/2011/04/05/programming-praxis-fortune/ for a version with comments):

   import Control.Monad
   import System.Environment
   import System.Random
   
   chance :: Int -> Int -> a -> a -> IO a
   chance x y a b = fmap (\r -> if r < x then a else b) $ randomRIO (0, y-1)
   
   fortune :: [a] -> IO a
   fortune = foldM (\a (n,x) -> chance 1 n x a) undefined . zip [1..]
   
   main :: IO ()
   main = putStrLn =<< fortune . lines =<<
          readFile . head . (++ ["fortunes.txt"]) =<< getArgs
   
3. Dave Webb said

   April 5, 2011 at 12:27 PM

   A Python solution:

   import random,sys
   filename = sys.argv[1] if len(sys.argv) > 1 else '/usr/games/lib/fortunes'
   
   with open(filename) as fortunes:
       print random.choice(list(fortunes)),
   
4. arturasl said

   April 5, 2011 at 12:46 PM

   Beauty of awk :

   #!/bin/awk
   BEGIN{srand()}
   {if(rand()<=1/++n)l=$0}
   END{print l}
   
5. Graham said

   April 5, 2011 at 3:10 PM

   My first solution is similar to Dave Webb’s, but I also wrote up an iterative
   function that will use less resources if the fortune file is large.

   #!/usr/bin/env python
   from random import choice, randrange, seed
   from sys import argv
   
   def whole_file(f):
   # easily written, good if f is smallish
       return choice(f.readlines())
   
   def iter_file(f):
   # good if f is large
       curr_line, n = None, 0
       for line in f:
           n += 1
           i = 0 if randrange(n) > 1 else 1
           curr_line = [curr_line, line][i]
       return curr_line
   
   def main(f, func=iter_file):
       print func(f)
       return None
   
   if __name__ == "__main__":
       seed()
       f_name = argv[1] if len(argv) > 1 else "fortunes.txt"
       with open(f_name) as f:
           main(f)
   
6. Graham said

   April 5, 2011 at 3:11 PM

   Woops, line 14 should read i = 0 if randrange(n) >= 1 else 1
7. Graham said

   April 5, 2011 at 8:08 PM

   After writing my above solution, I took this as an opportunity to play
   with pylint a sourcecode analyzer.
   My new version is available here.
8. Mike said

   April 5, 2011 at 8:09 PM

   Another variation on solutions posted by Dave and Graham.

   from collections import deque
   from itertools import count, compress
   from random import randint
   from sys import argv
   
   FORTUNES = 'fortunes.txt'
   
   with open(argv[1] if argv[1:] else FORTUNES, 'rt') as f:
      print deque(compress(f, (not randint(0,n) for n in count())), maxlen=1).pop()
   
9. Graham said

   April 6, 2011 at 2:57 PM

   Nice one Mike; I need to learn more about the itertools module.
   Quick question, though: randint(0, n) uniformly picks a random integer from [0, n]
   (inclusive), so doesn’t this use the probability 1/(n + 1) instead of 1/n?
10. Mike said

    April 6, 2011 at 6:32 PM

    @Graham. Yes, my program calculates the probability as 1/(n+1). However, n starts at 0.
    So, for fortune lines 0, 1, 2, …, the probabilities are 1/1, 1/2, 1/3, ….
    This is the same as n starting at 1 and calculating the probability as 1/n.
11. Ross said

    April 6, 2011 at 10:22 PM

    An version in Common Lisp:

    (defun fortune (filename)
      "Return a Unix V7 fortune"
      (with-open-file (s filename :direction :input)
        (loop :with fortune
              :for line = (read-line s nil)
              :while line
              :counting line :into counter
              :do (when (< (random counter) 1) (setq fortune line))
              :finally (return fortune))))

    and a completely golfed command line Perl version perl -ne 'rand($.)<1&&($l=$_)}{print$l' just because the awk version was still readable.
12. Graham said

    April 7, 2011 at 12:34 AM

    @Mike: My mistake! Thanks for clearing that up.
13. Khanh Nguyen said

    April 16, 2011 at 7:42 PM

    In F#,

    open System
    let rnd = new Random()
    let lines = System.IO.File.ReadAllLines("fortunes.txt")
    Seq.nth (rnd.Next(Seq.length lines)) lines
    
14. Fortune of Unix V7 implemented in Java said

    January 7, 2023 at 3:58 PM

    […] reimplemented a basic version of Fortune. This version prints to the standard output a randomly chosen line from a text file. You can […]

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