Processing 1.0 - Processing Discourse - randomize i in a for() construction

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Index › Programming Questions & Help › Syntax Questions › randomize i in a for() construction

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randomize i in a for() construction (Read 1153 times)

typovar

randomize i in a for() construction
Mar 24^th, 2008, 11:26am

I have used the collage-code from the Processing book to create my own collage. I loaded all images in an PImage[] array and made code more compact. But I want to "randomize" the order in which the images are loaded.

Now, every "page" holds the images in the same order. I want image 1 to appear on top of the stack as well. Here's the part of the code I'm reffering to:

Code:

page=new PImage[28];
for(int i=0;i<page.length;i++) {
    page[i]=loadImage("nyt_"+i+".jpg");  
    image(page[i], -page[i].width/2, -page[i].height/2);
   }

disablek YaBB Newbies Offline Posts: 48	Re: randomize i in a for() construction Reply #1 - Mar 26^th, 2008, 3:22am You could try generating a random int, insert that into a hash until that hash size is the size you want, and iterate through that as a sequence for the loading of images. i'm not sure if unique random numbers in a range is already possible in java.

typovar YaBB Newbies Offline Posts: 10 The Netherlands	Re: randomize i in a for() construction Reply #2 - Mar 26^th, 2008, 8:25am Somehow it makes sense, but can you give an example? I'm not a programmer and I still need examplecode to modify. I'm glad someone takes time to help me out. Thanks.

disablek YaBB Newbies Offline Posts: 48	Re: randomize i in a for() construction Reply #3 - Mar 26^th, 2008, 10:28am off the top of my head in pseudo code maybe like this while(x!=whatever-1){ int a=int(random(0,whatever)); if(!exists(a) in hash){ insert a in hash; x++; } } voila ... iterate thru that hash and load em up.

typovar

Re: randomize i in a for() construction
Reply #4 - Mar 26^th, 2008, 12:18pm

This is the complete code:
I tried to use your example, but it failed to execute.
Code:

float x, y, r, s; 
PImage[] page;
void setup(){
  size(800,600);
  smooth();
  background(0);
}
void draw(){
  fill(0);
  rect(0,0,width,height);
  noFill();
  page=new PImage[28];

// while(x!=whatever-1){
// int a=int(random(0,whatever));
// if(!exists(a) in hash){
// insert a in hash;
// x++;
// }} 

  for(int i = 0; i < page.length;i++) {
    page[i]=loadImage("nyt_"+i+".jpg");  
    x = random(width);
    y = random(height);
    s = random(0.4,0.8);
    tint(255, 220);
    r = random(-0.2,0.2); 
    pushMatrix();   
    translate(x,y);
    rotate(r);
    scale(s);
    image(page[i], -page[i].width/2, -page[i].height/2);
    popMatrix();
  }
  saveFrame("page_" + frameCount + ".jpg");
  if (frameCount == page.length) {
    exit();  
  }
}

koogy

Re: randomize i in a for() construction
Reply #5 - Mar 26^th, 2008, 7:47pm

move the initialisation of the page loop into the setup and it'll be much faster. you don't need load all the images on every loop.

for the randomness i'd have an array filled with 0 to n. then do a knuth shuffle on it and use shuffled_array[i] instead of i in your image() call.

http://en.wikipedia.org/wiki/Fisher-Yates_shuffle

(it's about 5 lines of code)

typovar YaBB Newbies Offline Posts: 10 The Netherlands	Re: randomize i in a for() construction Reply #6 - Mar 26^th, 2008, 10:06pm thanks! This is helpfull. All the random-stuff I tried ended up with a lot of processor/harddisk-noise from my pc. I'll do the knuth-shuffle tommorrow. And the Wallstreet-shuffle next year...

disablek YaBB Newbies Offline Posts: 48	Re: randomize i in a for() construction Reply #7 - Mar 27^th, 2008, 2:51am damn that's a good algorithm, i must get that book. pseudo code means it's not actual running code. It's just a easy method of verbalizing the algorithm without getting into the nitty gritty details of the syntax.

acapulco Junior Member Offline Posts: 63	Re: randomize i in a for() construction Reply #8 - Mar 27^th, 2008, 8:17am Indeed. It's a pretty nice algorithm the Knuth shuffle. I've never heard of it before, but it seems to be pretty intuitive. I'll have to find some applications for it then. Yey. :]

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