# Randomly pick one variable

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?

2 Likes

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;
}
``````
3 Likes

A shorter 1 using the ternary conditional operator `?:`: Processing.org/reference/conditional.html

``````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();
``````
2 Likes

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

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

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

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

I am thinking that pick can be = MIN_INT, is that wrong? Yes, if the 1st `a == -1 & b == 1` fails.

1 Like

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

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 and a vars holding our values. Let’s pick one at random.

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

This will look up either vars (= -1) or vars (= 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.

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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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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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Which one did you pick?

`:)`

1 Like

@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