How to make random generator not repeat twice the same number ?

[Declan Smith]

Try this.

This will create an array of consecutive numbers starting at zero going up to the length of your composition (in frames). The array is then randomly shuffled (shuffle routine courtesy of google) but with the random number seed being the same each time, so that each frame creates the same random sort order. The number returned from array is chosen by using the current frame number.

To see this work, put it on the source property of a text object.

You can use the numbers in the array as you wish, scale them whatever. Also, if you want them to hold for a number of frames, then just change how you extract the number from the array. i.e. if you want to hold a particular number for 5 frames, then change the last line to read something like:
numarray(Math.floor(ttf/5))

But the essence of the code below is that it generates a random number that doesn’t repeat.

function shuffle(o){
// Shuffle based on original code by Jonas Raoni Soares Silva
//https://jsfromhell.com/array/shuffle [v1.0]
seedRandom(1, timeless = true);
for(var j, x, i = o.length; i; j = parseInt(random() * i), x = o[--i], o[i] = o[j], o[j] = x);
return o;
}
max=timeToFrames(t = thisComp.duration + thisComp.displayStartTime, fps = 1.0 / thisComp.frameDuration, isDuration = false);
numarray=[];
for (i = 0; i <max; i++) {
numarray.push(i);
}
numarray=shuffle(numarray);
ttf=timeToFrames(t = time + thisComp.displayStartTime, fps = 1.0 / thisComp.frameDuration, isDuration = false);
numarray[ttf];


Declan Smith
https://www.madpanic.tv
After Effects CS6/ FCS3 / Canon 7D / Canon XL2 / Reason / Cubase

“it’s either binary or it’s not”

[Lionel Vicidomini]

Thanks for the answer.
I understand some parts of the expression.
As for the array, I understand that it is generated from the duration of the composition, i.e a 250 frames comp will give an array from 0 to 250.
You say to scale the array, but how ?
The expression works perfectly, except that I would like to specify myself the array, as simply as in the “random(minValOrArray, maxValOrArray)”, say from 1 to 15, without it being related to the duration of the comp.
When I put an array in the numArray part of the expression, it doesn’t seem to work…

[Declan Smith]

The expression as supplied generates random numbers that do not repeat. If you limit the numbers that you want the expression to return from 1-15, then by definition, you can only evaluate this 15 times before you will have to repeat a value.

So I am now not entirely sure what problem you are trying to solve.

If you want to limit the numbers that are generated to between 1-15 then you will need some additional mechanism to ensure they don’t repeat, i.e. holding the value for a number of frames, or changing the value based on a keyframe.

In order to specify your own values, I have added both min and max values, just set these to what you want. The for loop creates the array. (currently I have set min=1 max=15)

I have provided you two Options below.

Option 1 – Expression will repeat every max frames.
Just change the value of the interval (current set to 10)

Option 2 – Expression will pick a value based on the keyframe index. In other words you add keyframes where you want the value to change. Note that your maximum number of keyframes is determined by your ‘max’ value you specified. Uncomment the lines specified

function shuffle(o){
// Shuffle based on original code by Jonas Raoni Soares Silva
// https://jsfromhell.com/array/shuffle [v1.0]
seedRandom(1, timeless = true);
for(var j, x, i = o.length; i; j = parseInt(random() * i), x = o[--i], o[i] = o[j], o[j] = x);
return o;
}
//max=timeToFrames(t = thisComp.duration + thisComp.displayStartTime, fps = 1.0 / thisComp.frameDuration, isDuration = false);
min=1
max=3
numarray=[];
for (i = min; i <=max; i++) {
numarray.push(i);
}
numarray=shuffle(numarray);

// Option 1 - Will change value every 'interval' number of frames (but will repeat every 'max' * 'interval' frames
ttf=timeToFrames(t = time + thisComp.displayStartTime, fps = 1.0 / thisComp.frameDuration, isDuration = false);
interval=10;
numarray[Math.floor((ttf/interval) % max)];

// Option 2 - Will select based on keyframe position (uncomment the next four lines
//n = 0;
//n = nearestKey(time).index;
//if (key(n).time > time) n--;
//numarray[n % max];


Declan Smith
https://www.madpanic.tv
After Effects CS6/ FCS3 / Canon 7D / Canon XL2 / Reason / Cubase

“it’s either binary or it’s not”

[Xavier Gomez]

An alternative, built upon Dan Ebberts’ expression:

holdTime = 0.5;
n = 4;
t0 = inPoint;
t = time-t0;
STEPS = 1 + Math.floor(t/holdTime);

// initially generate a number in {0,1,..., n-1}
seedRandom(0,true);
idx = Math.floor(random(n));

// if (t>= holdTime)add something non zero, step after step
for(var step=1; step< STEPS; step++){
seedRandom(step, true);
idx = (idx + Math.floor(random(n-1)+1)) % n;}

//return
idx + 1;

[Lionel Vicidomini]

Both expressions work fine.
Actually, Xavier Gomez’s is what I was looking for, but Smith’s one can be very useful is other situation (the “shuffle” variable is very interesting)
Thanks to both of you !