Lingo in a Nutshell

List Utilities

Randomized Lists

The following handler creates a nonrepeating random list of n numbers (Refer to Chapter 8 for details on the random() function.) The trick is to place the numbers 1 through n into random locations throughout the list as it is built.

Example 6-23. Creating a List of Random Numbers

on randomNumberList n
  -- Initialize an empty list
  set myList = [ ]
    -- Create a list with the requested number of elements
repeat with x = 1 to n
   -- Insert the next number in a random place in the list
    addAt (myList, random(x), x)
  end repeat
  return myList
end randomNumberList

put randomNumberList (10)
-- [8, 10, 7, 5, 1, 3, 9, 4, 2, 6]

The following incorrect routine (which you’ll often see used) will likely result in some numbers being repeated in the list. It incorrectly adds random numbers that may already exist in the list because the random() function may generate the same number multiple times. See "How Random Is Random?" in Chapter 8 for details.

Example 6-24. Incorrect (Nonrandom) List Creation

on incorrectRandom n
    -- Initialize an empty list
  set myList = [ ]
   -- Create a list with the requested number of elements
  repeat with x = 1 to n
  -- Add a random number to the list
    add (myList, random(n))
  end repeat
  return myList
end incorrectRandom

put incorrectRandom  (10)
-- [9, 1, 6, 4, 4, 10, 2, 3, 9, 4]

This handler returns a randomized version of any linear list or property list, leaving the original list intact. Note that this randomizes an existing list, which differs from creating ...