This R package provides a simple way to make all sorts of dice rolls using syntax inspired from tabletop roleplaying games like Dungeons & Dragons.

# install.packages("remotes")
remotes::install_github("felixmil/rollr")

library(rollr)

roll_dice("1d12") # rolls one 12-sided dice

roll_dice("1d20+2") # roll one 20-sided dice then adds 2

roll_dice("2d10 + 1d4") # rolls two 10-sided dice and one 4-sided diced and sums their results 

roll_dice("4d6h3") # rolls four 6-sided dice and sum the 3 highests

roll_dice("2d20l1") # rolls two 20-sided dice and keeps the lowest one

in Dungeon & Dragons 5th Edition, ability scores are set by rolling 4d6 (four 6-sided dice) and keeping the 3 highest ones (ability scores can range between 3 and 18).

Let’s say we want to create a new character: Dunrill, a strong and muscular Dwarf. We roll our first set of 4 6-sided dice and keep the 3 highests.

library(rollr)

set.seed(42)

roll_results <- roll_dice("4d6h3", roll_history = TRUE) 
#> Evaluating "4d6h3" 
#> ==========
#> rolls: 1, 5, 1, 1
#> keeping 3 highest(s): 5, 1, 1
#> ==========
#>  Result is 7

That’s a 7. Now, the same roll (4d6h3) must be reproduced 5 more times:

more_roll_results <- replicate(5, roll_dice("4d6h3"))

all_results <- c(roll_results, more_roll_results)

print(all_results)
#> [1]  7  8 10 12  7 15

Now, we can assign these 6 values to Dunrill abilities (Strength, Dexterity, Constitution…) move on with character creation.

But were we lucky rolling these values: 7, 8, 10, 12, 7, 15 ?

To know that, we’ll simulate 9999 4d6h3 rolls and approximate the probability distribution.

random_rolls <- replicate(9999, roll_dice("4d6h3"))

Probability distribution for 4d6h3 looks like this:

Distribution’s mode is 13, however, the mean of our rolls is 9.83:

Features list derivated from Sidekick

• /r 1d8 + 2 - Roll one octahedron and add two.

• /r 1d8 + 4d6 - Roll one octahedron and four hexahedrons.

• /r 2d20h1 - Roll twice and keep the highest roll (D&D 5e advantage).

• /r 2d20h1 + 2 - Roll twice and keep the highest roll, with a modifier (D&D 5e advantage).

• /r 4d6h3 - Roll four hexahedrons and keep the highest three (D&D 5e ability roll).

• /r 2d20l1 - Roll twice and keep the lowest roll (D&D 5e disadvantage).

• /r 1d20r1 - Roll twenty, reroll on one (because halflings are lucky).

• /r 3d6! - Exploding dice.

• /r 2d6>=5 - Roll two hexahedrons and take only the ones that turned greater or equal to five (aka difficulty check). Prints the number of successes.

• /r 4d6=5 - So can this guy roll five?

• /r 3d10>=6f1 - oWoD roll: rolling one is a failure, rolling more failures than successes is a botch.

• /r 1d10>=8f1f2 - Rolling one or two is a failure.

• /r 4dF - Fudge/Fate dice.

• /r 1d10!>9 - Explode nine and ten.

• /r 3d10!>=8 - nWoD roll: tens explode, eights and up are treated like a success.

• /r 1d10t10 - If a ten is rolled then count it twice.

• /r repeat (4d6k3, 6) - Roll D&D 5e ability score six times (to generate a new character).

• /r repeat (d6, 3, brief) - In Nomine. 1, 1, 1.

• /r repeat (1d20+1, 5, short sum) - Sum the rolls.

• /r ova (5) - OVA. 6, 6, 1, 1, 1 = 12.

• Support all rolls syntax above
• Add function to replicate a dice command n times (don’t reparse dice command each time)
• Create Vignette (from Use case ?)