Select random elements from an array without repeats? - arrays

Question

edit: I can't believe I didn't catch this sooner. Turns out my problem was re-declaring my first variables over and over again, essentially starting the program fresh instead of continuing it. To fix it, I replaced the first two lines with this:
if (initialized === undefined) {
trace("INITIALIZING");
var MCs = [];
var lastPos = "intializer";
var initialized = 1;
}
Now it works like a charm. I feel like a noob for this one; sorry to anyone whose time I wasted. I'd post this as an answer to my own question, but it won't let me since I'm still new.
Original Post follows:
I'm trying to make a flash that will randomly choose an ad, play it, and then randomly play another. To that end, I've succeeded by shuffling an array, and then gotoAndPlay-ing the label in the first element of the array, and then removing that element. At the end of each ad is gotoAndPlay(1); with all the main code being on the first frame. If the array is empty, it rebuilds it and reshuffles it.
The problem is, I don't want it to repeat any ads until its run through all of them; I think I've got that down, but I'm not positive. Further, I don't want the last element in the array to be the same as the first in the new one, so the same ad won't ever show twice in a row. I'm trying to have it detect if the element it just used matches the one it's about to use, and reshuffle if that happens, but in my testing it continues to occasionally show the same ad twice in a row.
I'm obviously doing something wrong, but being entirely new to ActionScript3 (and in fact to flash) I'm having a lot of trouble identifying what it is. Here's what I have right now:
var MCs = [];
var lastPos = "intializer";
if (MCs.length == 0) {
MCs = reset();
if (lastPos == MCs[0]) {
while (lastPos == MCs[0]) {
MCs = reset();
}
}
}
if (MCs.length > 0) {
lastPos = MCs[0];
MCs.splice(0,1);
gotoAndPlay(lastPos+"MC");
}
function reset(){
var PrepMCs = new Array("Image1", "Image2", "Image3");
var WorkMCs = new Array(PrepMCs.length);
var randomPos:Number = 0;
for (var i:int = 0; i < WorkMCs.length; i++)
{
randomPos = int(Math.random() * PrepMCs.length);
WorkMCs[i] = PrepMCs.splice(randomPos, 1)[0];
}
return WorkMCs;
}
Personally, I'd rather just do this with JavaScript, HTML, and images; it'd be really simple. But for hosting/CMS reasons I don't have any control over, I'm limited to a single file or a single block of code; I can't host anything externally, which as far as I can tell leaves Flash as my best option for this.
Any help would be greatly appreciated, thanks! If I've done something horribly, horribly wrong, and it's a wonder this even runs at all, don't hesitate to tell me!
edit: It just occurred to me, it is perfectly fine if the second run is in the same order as the first run, etc. The main thing is, it needs to be random. This is probably much easier to implement.
edit 2: MASSIVE DERP HERE. Every time it runs, it re-initializes MCs and lastPos... in other words, it's shuffling every time and starting over. What I should be researching is how to only run a line of code if a variable hasn't been initialized yet.

Answer 1

Blatantly stealing from #32bitKid, this is my version.
The main problem I have with his solution is the push/splice idea. As much as possible, I like to create once, and reuse. Shrinking and growing arrays is bulky, even if effective.
Also, this method does not re-order the array, which may or may not be valuable.
BTW, I like the way that he prevents a repeat of the previous item ("almost empty").
So here is another method:
package
{
public class RandomizedList
{
private var _items:Array;
private var idxs:Array;
private var rnd:int;
private var priorItemIdx:int;
private var curIdx:int;
public function RandomizedList(inarr:Array)
{
items = inarr;
}
private function initRandomize():void
{
idxs = new Array();
//Fisher-Yates initialization (http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle):
idxs[i] = 0;
for (var i:int = 1; i < items.length; i++)
{
rnd = int(Math.random() * (i + 1));
idxs[i] = idxs[rnd];
idxs[rnd] = rnd;
}
curIdx = 0;
priorItemIdx = -1;
}
private function randomize():void
{
var tempint:int;
//Fisher-Yates (http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle):
for (var i:int = items.length; i >= 1; i--)
{
rnd = int(Math.random() * (i + 1));
tempint = idxs[i];
idxs[i] = idxs[rnd];
idxs[rnd] = tempint;
}
curIdx = 0;
}
public function next():void
{
if (curIdx >= idxs.length)
{
randomize();
}
if (items.length > 1 && priorItemIdx == idxs[curIdx])
{
curIdx++;
}
priorItemIdx = idxs[curIdx++];
return items[priorItemIdx];
}
public function get items():Array
{
return _items;
}
public function set items(value:Array):void
{
_items = value;
initRandomize();
}
}
}

Answer 2

I would use a utility class like this to abstract out the behavior I wanted:
import flash.text.TextField;
class Randomizer {
private var unused:Array = [];
private var used:Array;
public function Randomizer(playList:Array) {
used = playList;
}
public function next():* {
// If almost empty, refill the unused array
if(unused.length <= 1) refill();
// Get the first item off the playList
var item:* = unused.shift();
// Shove it into the bucket
used.push(item);
// return it back
return item;
}
public function refill():void {
var i:int;
// Fisher-Yates shuffle to refill the unused array
while(used.length > 0) {
i = Math.floor(Math.random() * used.length)
unused.push(used.splice(i,1)[0])
}
}
}
Notice that it refills the unused array when the unused array still has one item in it, this makes it impossible for the last result to repeat twice in a row. This will return each item once before before looping, and will never repeat the same item twice.
You would use it by saying something like:
var ads:Randomizer = new Randomizer(["Image1", "Image2", "Image3"]);
ads.next(); // will return something
ads.next(); // will return something
ads.next(); // will return something
ads.next(); // will return something
// Keep going into infinity...
There is a little test example of this code working here.

Answer 3

See if this makes any sense
//create your array of all your ad names/frame labels
var PrepMCs:Array = new Array("Image1", "Image2", "Image3");
var shuffledMCs:Array = [];
//store the name of the last played ad in this var
var lastAdPlayed:String;
//shuffle the array
shuffleArray(PrepMCs);
function shuffleArray(arrayToShuffle:Array):void {
//clear the array
shuffledMCs = [];
var len:int = arrayToShuffle.length;
for(var i:int = 0; i<len; i++) {
shuffledMCs[i] = arrayToShuffle.splice(int(Math.random() * (len - i)), 1)[0];
}
//test to see if the new first ad is the same as the last played ad
if (lastAdPlayed == shuffledMCs[0]) {
//reshuffle
shuffleArray(PrepMCs);
} else {
lastAdPlayed = [0];
trace(shuffledMCs);
playAds();
}
}
//after each ad has played, call this function
function playAds():void {
if (shuffledMCs.length > 0) {
gotoAndPlay(shuffledMCs[0]);
shuffledMCs.splice(0,1);
} else {
//array is empty so we have played all the ads
shuffleArray(PrepMCs);
}
}