Randomly pick one variable

Processing Beginners
1

Is there a way to randomly pick between two values. For example, randomly pick a or b, not anything in between, and if possible, do this when a = -1 and b = 1?

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2

Of course it is. I’m not sure I understood what you meant. There are shorter ways to do this, but less readable and understandable

int ran;
if(a == -1 && b == 1) {  //check if a = -1 and b = 1
  if(random(2) < 1) { //Generate random number between 0 and 2. If < 1 set ran=a,
    ran = a;
  } else { //else random(2) is >= 1. set ran=b
    ran = b;
}
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3

A shorter 1 using the ternary conditional operator ?:: :wink:

int a = -1, b = 1, pick = MIN_INT;
if (a == -1 & b == 1)  pick = random(2) < 1? a : b;

println(pick);
exit();

int a = -1, b = 1;
int pick = a == -1 & b == 1? random(2) < 1? a : b : MIN_INT;

println(pick);
exit();
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4

Thanks, they worked, I do have another question what MIN_INT mean?

5

Processing.GitHub.io/processing-javadocs/core/processing/core/PConstants.html#MIN_INT

Some arbitrary value to flag it failed to pick 1 of the 2 random() values. :nerd_face:

6

Got it so if a, and b are not = to 1, and -1, MIN_INT would be true, but wouldn’t it be printed in the console too?

7

print() to console is merely to log what happened.

Much probably you’ve got something else in mind when MIN_INT is the result.

8

I am thinking that pick can be = MIN_INT, is that wrong? :thinking:

9

Yes, if the 1st a == -1 & b == 1 fails.

1 Like
10

If it fails then the print would print MIN_INT because it is the only thing that is true now, right?

11

This thread is assuming that you meant this as a state condition. But I suspect you just mean that these are the ranges you want. Does the value of a ever change?

Or do you just mean that you want to flip a coin, heads = -1, tails = 1? Possibly with arbitrary values on the coin?

Consider:

random(1) : 0.41… 0.74… 0.22… 0.52… 0.10… 0.87…
round(random(1)) : 0 1 0 0 1 1 1 0 1 0 1 1 0 0 …
…or (int)random(2) : 0 1 0 0 1 1 1 0 1 0 1 1 0 0 …
2 * round(random(1)) : 0 2 0 0 2 2 2 0 2 0 2 2 0 0 …
2 * round(random(1)) - 1 : -1 1 -1 -1 1 1 1 -1 1 -1 1 1 -1 -1 …

Now, this is just computing a random 1 or -1 – it isn’t picking a variable at random. However, there are many ways to connect a choice between two and a random number. For example:

int[] vars = new int[] { -1, 1 };

Now we have a vars[0] and a vars[1] holding our values. Let’s pick one at random.

println( vars[ (int)random(2) ] )

This will look up either vars[0] (= -1) or vars[1] (= 1). Now you could put any values in there, like { -13, 4 } and vars[ (int)random(2) ] would always return one of those two values at random.

1 Like
12

I am trying to the heads or tails method. I understand the first method and the last one, but I don’t get this:

Can you please explain it for me?

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13

Try wrapping each one in println() to see what it does. Maybe wrapping that in a for loop to see it multiple times.

for (int i=0; i<10; i++) {
  println(
    (int)random(2)
  );
}

random(x) returns a random float in the range 0-x. (int) casts the float to an integer.

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14

Which one did you pick?

:)

1 Like
15

@glv I decide to pick the third one :

int[] vars = new int[] { -1, 1 };
println(vars[(int)random(2) ] );

but they are all good.

3 Likes