riddler-die-reroll.Rmd

---
title: "The Riddler: Rerolling a die"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

```{r}
library(tidyverse)

start <- 1:6

next_rolls <- sample(start, replace = TRUE)

simulate_roll <- function(num_sides = 6) {
  rolls <- accumulate(1:1000, function(x, ...) {
    result <- sample(x, replace = TRUE)
    
    if (length(unique(result)) == 1) {
      done(result)
    } else {
      result
    }
  }, .init = 1:num_sides)
  
  length(rolls) - 1
}

simulations4 <- replicate(1e6, simulate_roll(4))

mean(simulations)

tibble(simulations) %>%
  count(simulations, sort = TRUE)
```

On average, it takes 9.666 rolls to get the same number on all sides.

```{r simulations_crossed}
simulations_crossed <- crossing(trial = 1:20000,
                                num_sides = 2:10) %>%
  mutate(simulation = map_dbl(num_sides, simulate_roll))
```

```{r}
summarized <- simulations_crossed %>%
  group_by(num_sides) %>%
  summarize(average_roll = mean(simulation),
            variance_roll = var(simulation),
            sd_roll = sd(simulation),
            cov = sd_roll / average_roll)

summarized %>%
  ggplot(aes(num_sides, average_roll)) +
  geom_point() +
  geom_line() +
  expand_limits(y = 0)

lm(average_roll ~ num_sides, summarized)

simulations_crossed %>%
  ggplot(aes(simulation)) +
  geom_histogram(binwidth = 1) +
  facet_wrap(~ num_sides, scales = "free_y")
```