Reddit Probability Bot

Update: Heroku's free tier has been discontinued, so the bot is no longer hosted.

A bot built in Python that performs basic probability tasks, such as rolling dice or flipping coins. You can view the bot here.

Usage

You must first call the bot with /u/ProbabilityBot_, and then use one (or multiple) of the following commands. You can only have one command per line, and it must be at the beginning of the line.

If you want to play around with this bot, I'd recommend making a thread in /r/test, which is designed for testing things like Reddit bots.

!roll

This command rolls one or more dice, and provides a breakdown of what you rolled. By default, it rolls a single 6-sided die. The maximum number of dice you can roll at once is 50 and the maximum number of sides a given die can have is 10000.

Arguments

You can specify how many and what kind of dice to using standard dice notation:

• X: rolls X 6-sided dice

• dY: rolls a single Y-sided die

• XdY: rolls X Y-sided dice

• XdY+Z: rolls X Y-sided dice and adds Z to the total

• XdY-Z: rolls X Y-sided dice and subtracts Z from the total

• XdY*Z: rolls X Y-sided dice and multiplies the total by Z

In addition, you can use these flags:

• --nb: no breakdown of your rolls is provided and the maximum number of dice you can roll at once is increased to 1000

• --s: sorts the breakdown of your rolls (descending)

• --a: calculates the average result of your rolls

• --dl: discards the lowest roll

• --dl N: discards the lowest N rolls

• --dh: discards the highest roll

• --dh N: discards the highest N rolls

• --tl N: instead of summing the rolls, it counts the number of rolls lower than N (ie. target sum)

• --te N: instead of summing the rolls, it counts the number of rolls equal to N

• --th N: instead of summing the rolls, it counts the number of rolls higher than N

• --el N: if a roll is lower than N, it is rerolled, and the previous roll is kept (ie. exploding rolls)

• --ee N: if a roll is equal to N, it is rerolled, and the previous roll is kept

• --eh N: if a roll is higher than N, it is rerolled, and the previous roll is kept

• --rl N: if a roll is lower than N, it is rerolled, and the previous roll is discarded (ie. rerolls)

• --rl N: if a roll is equal to N, it is rerolled, and the previous roll is discarded

• --rl N: if a roll is higher than N, it is rerolled, and the previous roll is discarded

!fate

Rolls Fate (or Fudge) dice. By default, it rolls 4 dice.

Arguments

You can specify how many kind of dice to using standard dice notation:

• X: rolls X Fate dice

• +Y: rolls 4 Fate dice and adds Y to the total

• -Y: rolls 4 Fate dice and subtracts Y from the total

• *Y: rolls 4 Fate dice and multiplies the total by Y

• X+Y: rolls X Fate dice and adds Y to the total

• X-Y: rolls X Fate dice and subtracts Y from the total

• X*Y: rolls X Fate dice and multiplies the total by Y

In addition, you can use these flags:

• --nb: no breakdown of your rolls is provided and the maximum number of dice you can roll at once is increased to 1000

!flip

Flips one or more coins. By default, it flips a single coin.

Arguments

• N: flips N coins

!pi

Approximates pi. The probability of two random numbers being coprime is 6/π² (source). Therefore, if we generate N pairs of random numbers, count how many of them are coprime, and do a little math, we can approximate PI. By default, it uses 1000 pairs of random numbers. The maximum number of pairs you can do is 100000.

Arguments

• N: use N pairs of random numbers

Formatting

If a roll is discarded, it is struck-through: 5

If a roll matches the target, it is bolded: 5

If a roll rerolled, it has inline code formatting: 5

Examples

If you commented:

/u/ProbabilityBot_
!roll
!roll 5d7
!roll d10
!roll 12d5+4
!roll 6d7-9
!roll 6d7*2
!roll 25d250 --s --a
!roll 500d20 --nb --a
!roll 10d20 --dl 5
!roll 10d20 --dh 3
!fate
!fate +3
!fate -2
!flip
!flip 40
!pi
!pi 4000

You would get a reply like:

You rolled 1.
You rolled 17. Breakdown: (4, 1, 5, 4, 3).
You rolled 6.
You rolled 44. Breakdown: (3, 4, 1, 2, 5, 1, 3, 5, 3, 4, 5, 4) + 4.
You rolled 11. Breakdown: (3, 2, 5, 5, 4, 1) - 9.
You rolled 50. Breakdown: (2, 5, 2, 7, 3, 6) * 2.
You rolled 115, with an average of 9.5833. Breakdown: (20, 18, 17, 14, 13, 8, 7, 6, 5, 5, 1, 1).
You rolled 4827, with an average of 9.6540.
You rolled 81. Breakdown: (~~2~~, ~~8~~, ~~7~~, 15, 16, ~~11~~, 20, ~~1~~, 11, 19).
You rolled 51. Breakdown: (12, ~~16~~, 13, 2, 2, 10, ~~18~~, ~~15~~, 4, 8).
You rolled -1. Breakdown: (0, 0, -, 0).
You rolled 3. Breakdown: (-, 0, +, 0) + 3.
You rolled -1. Breakdown: (+, 0, -, +) - 2.
You got tails.
You got 20 heads and 20 tails.
With 1000 pairs, I approximated PI as 3.194383.
With 4000 pairs, I approximated PI as 3.140759.