1. // shuffle array
2. int[] a  = new int[3];
3. int[] a2 = new int[3];
4. //
5. void setup() {
6.   size (200, 200);
7.   // init
8.   for (int i=0; i<a.length; i++) {
9.     a[i] = i+1;
10.   } // for
11.   // shuffle
12.   arrayCopy(a, a2);
13.   randomize(a2);
14.   /* the result: either
15.    1 2 3 or
16.    1 3 2 or
17.    2 1 3 or
18.    2 3 1 or
19.    3 1 2 or
20.    3 2 1
21.    */
22. } // func
23. //
24. void draw() {
25.   background (0);
26.   // output
27.   print("the intial array: ");
28.   display(a, 19); //displays 1 2 3
29.   print("randomized array: ");
30.   display(a2, 39); //displays 1 2 3
31.   text ("Press any key to shuffle.", 10, 59);
32.   if (keyPressed || mousePressed) {
33.     randomize(a2);
34.   } // if
35. } // func
36. //
37. //method for display
38. void display(int[] arr, int intLineY) {
39.   for (int i=0; i<arr.length; i++) {
40.     print(arr[i]+" ");
41.     text (arr[i]+" ", i*20+10, intLineY);
42.   } // for
43.   println();
44. } // func
45. //
46. //method for randomizing
47. void randomize (int[] arrMy) {
48.   for (int k=0; k < arrMy.length; k++) {
49.     // Goal: swap the value at pos k with a rnd value at pos x.
50.     // Make rnd index x
51.     int x = (int)random(0, arrMy.length);    
52.     // swap pos k and x
53.     arrMy = swapValues(arrMy, k, x);
54.   } // for
55.   // display(a, 39);
56.   // return arrMy;
57. } // func
58. //
59. int[] swapValues (int[] myArray, int a, int b) {
60.   // Goal: swap the value at pos a with a value at pos b in
61.   // Array myArray, return the changed array. 
62.   // save current value from pos/index a into temp
63.   int temp=myArray[a];
64.   // overwrite value at current pos a with value at index b
65.   myArray[a]=myArray[b];
66.   // finish swapping by giving the old value at pos a to the
67.   // pos b.
68.   myArray[b]=temp;
69.   // return the changed array
70.   return myArray;
71. } // func
72. //

1. // Generate a list of random indices
   
2.  // http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle 
3. // inside-out algorithm 
4. for (int i = 1; i < indices.length; i++) 
5. {
6.  int j = int(random(0, i+1)); 
7.  indices[i] = indices[j];
   
8.  indices[j] = i; 
9. }

nice but when it's swapping we rather need

1. // Generate a list of random indices
2. // http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
3. // inside-out algorithm
4. for (int i = 1; i < positions.length; i++)
5. {
6. int j = int(random(0, i+1));
7. int dummy = positions[i];
8. positions[i] = positions[j];
9. positions[j] = dummy;
10. }

Greetings, Chrisir