Conway's game of life in R

game_of_life.R

start_game <- function(side_length) {
  # Boards are always square
  x <- rep(c(TRUE, FALSE), length.out = side_length^2)
  
  # Generate random probability for cells to start alive or dead
  p <- runif(min = 0, max = 1, n = side_length^2)
  
  # Set up the board
  board <- sample(x, size = side_length^2, replace = TRUE, prob = p)
  
  # Pre-calculate neighbor squares for all grid positions
  neighbors <- purrr::map(1:length(board), ~calc_neighbors(.x, side_length))
    
  game <- (list(board = board,
              neighbors = neighbors))
  
  # Game loop
  for(i in seq_along(1:1E3)) {
    draw_board(game$board)
    Sys.sleep(0.05)
    game <- update_game(game)
  }
}

calc_neighbors <- function(idx, side_length) {
  # Given an index, generate its neighbors
  out <- c(
    idx + 1,
    idx - 1,
    idx + side_length - 1,
    idx + side_length,
    idx + side_length + 1,
    idx - side_length - 1,
    idx - side_length,
    idx - side_length + 1
  )
  
  # Handle edge cases
  # The values to remove are based on the order in the "out" object
  rem <- c(rep(TRUE,8))
  
  if (idx %% side_length == 0){
    # Right edge
    rem[c(1,5,8)] <- FALSE
  }
  
  if (idx %% side_length == 1) {
    # Left edge
    rem[c(2,3,6)] <- FALSE
  }
  
  if (idx <= side_length) {
    # Top edge
    rem[6:8] <- FALSE
  }
  
  if (idx > (side_length^2 - side_length)) {
    # Bottom edge
    rem[3:5] <- FALSE
  }
  
  # This (accidentally) treats the world as wraparound
  
  return(out[which(rem)])
}

draw_board <- function(board) {
  side_length <- sqrt(length(board))
  image(matrix(board, ncol = side_length))
}

update_game <- function(game) {
  neighbor_counts <- purrr::imap(game$board, ~{
    sum(game$board[game$neighbors[[.y]]])
  }) |>
    unlist()
  
  #---- DA RULEZ ----
  # Any live cell with two or three live neighbours survives.
  # Any dead cell with three live neighbours becomes a live cell.
  # All other live cells die in the next generation. Similarly, all other dead cells stay dead.
  new_board <- purrr::map2(game$board, neighbor_counts, ~{
    if(.x == TRUE) {
      # Live cell
      if(.y ==2 || .y == 3) {
        TRUE
      } else { FALSE }
    } else if (.x == FALSE) {
      # Dead cell
      if(.y == 3) {
        TRUE
      } else { FALSE }
    } 
  }) |> unlist()
  
  # No need to change/recalculate neighbors
  return(list(board = new_board,
              neighbors = game$neighbors))
}