How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

Programming Questions

jlwarren26

How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

in Programming Questions • 11 months ago

Hi,

I am reading in information from a file into an arrayList. This list consists of strings. I am having one of those "when I see the solution I'll feel really stupid" moments. I know how to use random() and I know how to use randomSeed(). For example:

String[] words = {

"apple", "bear", "cat", "dog", "yak", "pear", "bat", "antelop"

};

int index = words.length;

randomSeed(2);

for (int i=0; i < index; i++) {

int r = (int) random (index);

println (words[r]);

}

But this doesn't ensure that each string in words [ ] is used once and only once (ie: some strings are used more than once while some aren't represented at all). I am looking for a way to randomize my array based on different seeds, while ensuring that each new permutation includes all the elements from the original array and only uses them once.

Any suggestions would be greatly appreciated.

Thanks,

Replies(9)

PhiLho

Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

What you want actually is to shuffle the array. Search this word in the forum and you will get several examples.

jlwarren26

Re: Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

@PhiLho

Thanks for your quick reply. Yea I've been thinking about this. I have used/created a shuffle before in a previous program that I made (seen below):

//create method to shuffle array

void shuffle (int[] shuffleArray) {

int holder; //holder to help swap #'s

int pick; //pick other # in array

//swap current item in current postion 'i' with the item in a random position in the array

for (int i=0; i< shuffleArray.length; i++) {

holder = shuffleArray[i]; //assign item at current pos to temp

pick = (int) random(shuffleArray.length - 1); //choose random # within the bounds of the array to be used for # swap

//don't allow a position # to switch with itself

if (pick != i) {

shuffleArray[i] = shuffleArray[pick];

} //end if

else {

pick = pick + 1;

shuffleArray[i] = shuffleArray[pick];

}//end else

shuffleArray[pick]= holder;

}//end for

}//end shuffle

The issue is that I am creating a program for an experiment that I will be running. There will be a start button on the screen. When this is clicked the current time will be written to a file and an entry ('prompt') from my array list will be drawn on the screen along with a 'next' button (array list will only contain 6 strings). When a user is done with the current prompt they can hit next and it will present the next prompt from the array list. This will continue until they are at the last prompt where the next button will be replaced by the finished button. When they click 'finished' the time will be written to the same file.

Since each participant in my experiment will be going through 5 periods I need a way to randomize this array (shuffle) it before the process is repeated. However, I need these 5 shuffled arrays to be the same for each participant. So in period one, every participant will see the array in the same order, then in period two they will see a new (shuffled) version of that array but I need a way for all participants to see that exact same shuffled array... and so on.

I suppose I could simply make 5 different shuffled version of my array in advance and save them as different arrays (arrayPeriod1, arrayPeriod2, ...), but for some reason that doesn't really seem that efficient. Is there perhaps a better way to do this?

Thanks again,

jlwarren26

Re: Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

Also, I need to ensure that every time I run this program (today, a week from now, etc) the randomized arrays shown for each period will be exactly the same which is why I was trying to combine the seeding idea to my current design... just as an fyi

If I simply use this method:

"I suppose I could simply make 5 different shuffled version of my array in advance and save them as different arrays (arrayPeriod1, arrayPeriod2, ...), but for some reason that doesn't really seem that efficient."

then every time I run my program these arrays will be initialized in a new way (shuffle will randomize in different way), which is exactly what I'm trying to avoid.

PhiLho

Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

" that doesn't really seem that efficient"
Don't worry about this unless there is a real performance issue;

You shown you know how to use randomSeed(). Your shuffle algorithm uses random(). So you can use both to do a repeatable shuffling.

jlwarren26

Re: Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

thanks

hahah yea... that is what I'm trying to do, but for some reason I am having trouble with the logic/syntax. As in previous comment:

"Also, I need to ensure that every time I run this program (today, a week from now, etc) the randomized arrays shown for each period will be exactly the same which is why I was trying to combine the seeding idea to my current design... just as an fyi

If I simply use this method:

"I suppose I could simply make 5 different shuffled version of my array in advance and save them as different arrays (arrayPeriod1, arrayPeriod2, ...), but for some reason that doesn't really seem that efficient."

then every time I run my program these arrays will be initialized in a new way (shuffle will randomize in different way), which is exactly what I'm trying to avoid."

jlwarren26

Re: Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

Any advice on how I can achieve this? Is there a simple example anywhere on how to combine these?

-JW

PhiLho

Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

I am sorry, my brain is still sleeping, apparently, I have some difficulty to understand where your problem is, actually.
Maybe that's something trivial. I am not sure if your problem is purely algorithmic or if it needs to define some procedure.

I will try to make a little specification.
When you start the sketch, you want either a new sequence (a new randomization of the array) or to load a known one.
The first case is simple: just take a random number, for example the current time stamp, as new seed:
Date d = new Date();
int seed = (int) d.getTime();
Now, if you judge you have a good sequence, or just one you need to keep, you just have to save the seed for this sequence to be able to reproduce it.
A way to do that is to use saveStrings(): load the previous text file, add this seed with an identifier, save it.
When you need to reproduce a sequence, load the file, find the corresponding identifier, and use the associated seed.

I don't give examples because I am not sure I described correctly your need, but the above should be rather simple to do.
You need to define your identifier, ie. a way to describe your sequence. Eg. with a simple number (nth sequence), a date, something...

jlwarren26

Re: Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

Thanks again for taking the time to provide feedback. I'll be looking into it :)

rbrauer

Re: How can I use randomSeed to produce multiple variations of an array while using all elements of array ONLY once?

11 months ago

Is this something like what you're looking for?

String[] words;

void setup() {
  noLoop();
  
  words = new String[]{ 
    "apple", "bear", "cat", "dog", 
    "yak", "pear", "bat", "antelop"
  };
}

void draw() {
  println(shuffleWithSeed(words, 0));
}

String[] shuffleWithSeed(String[] orig, int seed) {
  ArrayList<String> aa, bb;
  aa = new ArrayList<String>();
  bb = new ArrayList<String>();
  String[] ret = new String[orig.length];
  
  randomSeed(seed);
  aa.addAll(Arrays.asList(orig));
  while(aa.size() > 0)
    bb.add(aa.remove((int)random(aa.size())));
  bb.toArray(ret);
  return ret;
}

Top Reply