    ## R Script Sample File
    ## Source: http://www.rexamples.com

    ## Basics
    a <- 42
    A <- a * 2  # R is case sensitive
    print(a)
    cat(A, "\n") # "84" is concatenated with "\n"
    if(A>a) # true, 84 > 42
    {
      cat(A, ">", a, "\n")
    }

    ## Functions
    Square <- function(x) {
      return(x^2)
    }

    print(Square(4))
    print(Square(x=4)) # same thing

    DoSomething(color="red",number=55)

    ## Countdown
    countdown <- function(from)
    {
      print(from)
      while(from!=0)
      {
        Sys.sleep(1)
        from <- from - 1
        print(from)
      }
    }

    countdown(5)

    ## Reading user input
    readinteger <- function()
    {
      n <- readline(prompt="Enter an integer: ")
      n <- as.integer(n)
      if (is.na(n)){
        n <- readinteger()
      }
      return(n)
    }
    print(readinteger())

    readinteger <- function()
    {
      n <- readline(prompt="Enter an integer: ")
      if(!grepl("^[0-9]+$",n))
      {
        return(readinteger())
      }

      return(as.integer(n))
    }
    print(readinteger())

    ## Guess a random number game
    readinteger <- function()
    {
      n <- readline(prompt="Enter an integer: ")
      if(!grepl("^[0-9]+$",n))
      {
        return(readinteger())
      }
      return(as.integer(n))
    }

    # real program start here

    num <- round(runif(1) * 100, digits = 0)
    guess <- -1

    cat("Guess a number between 0 and 100.\n")

    while(guess != num)
    {
      guess <- readinteger()
      if (guess == num)
      {
        cat("Congratulations,", num, "is right.\n")
      }
      else if (guess < num)
      {
        cat("It's bigger!\n")
      }
      else if(guess > num)
      {
        cat("It's smaller!\n")
      }
    }

    ## Lists
    sum(0:9)
    append(LETTERS[1:13],letters[14:26])
    c(1,6,4,9)*2
    something <- c(1,4,letters[2])  # indices start at one, you get (1,4,"b")
    length(something)

    ## Pipe
    diamonds %>%
      filter(price > 1000) %>%
      group_by(cut) %>%
      tally() %>%
      rename(tally = n) %>%
      arrange(-tally) %>%
      mutate(pct = tally / sum(tally)) -> df

    ## ggplot2
    plot = ggplot(diamonds, aes(x = price, y = carat)) +
      geom_point(alpha = 0.3, colour = 'steelblue') +
      labs(
        title = "ggplot diamonds",
        x = "Price, $",
        y = "Carat"
      ) +
      facet_wrap(~ cut) +
      theme_minimal()

    plot + coord_flip()