Useful Packages & Functions

This page offers a quick reference for R packages, built-in functions, and custom helper functions that I regularly use in AOC challenges.

Packages

Concept	Package Name	Example
Input Text Parsing	unglue	2020 Day 2
Graphs	igraph, tidygraph, ggraph	2020 Day 10
Memoization	memoise	2021 Day 21
64-Bit Integers	bit64	2024 Day 17
Sets & Intervals	sets	2021 Day 22
Geometry	sf	2022 Day 15
Primes, GCD, LCM	numbers	2020 Day 13

Built-In

Scientific Notation

Disable scientific notation to display all digits of large numbers:

options(scipen = 999)

Polar Coordinates

2D coordinates can be represented as complex numbers, easing common calculations such as addition, subtraction, distances, and angles:

z = complex(real = x, imaginary = y)

Pipes

Columns of a data frame can be passed through a pipe into a function that takes vector input by using the with function:

iris |> 
  with(cor(Sepal.Length, Sepal.Width))

Base N

Convert string representations of numbers in any base to integers using the strtoi function:

strtoi("0xff", base = 16L)
strtoi("1010", base = 2L)

Binary

Convert 32-bit integers to binary representation using intToBits:

intToBits(5)

Run Length

Calculate the length of continuous runs using rle. Convert a list of values and run lengths back to a single vector using inverse.rle.

x <- c(10, 10, 10, 10, 10, 9, 9, 9, 9, 8, 8, 8, 7, 7, 6)
rle(x)
inverse.rle(rle(x))

Snippets & Custom Functions

Read Matrix

Read text input directly into a matrix by using a combination of read.table and as.matrix:

input <- read.table(filepath) |> 
  as.matrix() |> 
  unname()

Print Compact Matrix

Display fixed-width matrices in a compact format, with no spaces between cells:

mtx_compact <- function(mtx) { 
  mtx |> 
    apply(1, str_flatten) |> 
    cat(sep = "\n")
}

Example:

c("#", "#", "#", "#", ".", '#', '#', '.', '#', "#", "#", "#") |> 
  matrix(nrow = 3) |> 
  mtx_compact()

####
#..#
####

Visualize Matrix as Image

Print matrices as a colored pixel image:

mtx_image <- function(mtx, palette = NULL, palette_fun = viridis::mako) {
  
  # If a color palette is not supplied, generate one
  if (is.null(palette)) {
    palette <- switch(typeof(mtx),
      "integer"   = palette_fun(max(mtx) - min(mtx) + 1),
      "double"    = palette_fun(100),
      "character" = palette_fun(length(unique(c(input))))
    )
  }
  
  # Convert character matrix to integers
  if (is.character(mtx)) {
    mtx <- mtx |> 
      match(factor(mtx)) |> 
      matrix(ncol = ncol(mtx))
  }
  
  # Transpose & flip matrix so that pixels are displayed in intended order
  image(
    t(mtx)[, nrow(mtx):1], 
    col = palette,
    asp = nrow(mtx) / ncol(mtx), 
    axes = FALSE
  ) 
}

Example:

round(runif(12, max = 100)) |> 
  matrix(nrow = 3) |> 
  mtx_image()