R/fibonacci.R

In Paul-James/pjames: Local Helper Functions

#' Calculate a fibonacci sequence
#'
#' Takes a sequence length and any two positive numbers in order to produce a fibonacci sequence. The fibonacci sequence is returned as a vector of numbers.
#'
#' If using the default first and second numbers of \code{0} and \code{1} \R will return \code{Inf} starting at element number \code{1478}.
#'
#' @param seq_length The length of the sequence as a number. The sequence length has to be greater than or equal to 2 (\code{seq_length >= 2}). The default is \code{10}.
#' @param first_num The starting point of the sequence. Use any positive number that comes before second_num (\code{first_num < second_num}). The default is \code{0}.
#' @param second_num The next number in the sequence after first_num. Use any positive number that comes after first_num (\code{second_num > first_num}). The default is \code{1}.
#'
#' @keywords fibonacci sequence math science nature
#'
#' @examples \dontrun{
#' fibonacci('eight', 2, -1)  # wrong #1
#' fibonacci(8, 2, -1)  # wrong #2
#' fibonacci(8, 2, 1)  # wrong #3
#' fibonacci(8, 2, 2) # wrong #4
#' }
#' fibonacci(8, 10, 12)  # correct!
#' fibonacci(seq_length = 20, first_num = 10, second_num = 15)  # yay!
#' fibonacci(30)
#' fibonacci()
#'
#' fibonacci(1500)[1477]
#' fibonacci(1500)[1478]
#' fibonacci(1500)[1500]
#'
#' @rdname fibonacci
#' @export

fibonacci <- function(
    seq_length = 10
  , first_num  = 0
  , second_num = 1
  ){

  # MAKE SURE THERE ARE ONLY NUMBERS AS PARAMETERS
  if(!is.numeric(c(first_num, second_num, seq_length))){
    stop("Whoah there. You used a non-number as a paramerter. Check yourself and only use numbers.")
  }
  # MAKE SURE ALL PARAMETERS ARE GREATER THAN 0
  if(sum(c(first_num, second_num, seq_length) < 0) > 0){
    stop("Only use positive numbers please. Muchas gracias!")
  }
  # MAKE SURE THE SEQUENCE LENGTH IS 2 OR MORE
  if(seq_length < 1){
    stop("Make sure your sequence length is 1 or more you silly goose.")
  }
  # MAKE SURE THE SECOND NUMBER IS LARGER THAN THE FIRST
  if(second_num - first_num <= 0){
    stop("Make sure your second number is bigger than your first number slick.")
  }


  if(seq_length < 2){

    first_num

  } else if (seq_length == 2){

    c(first_num, second_num)

  } else {

    fibo_seq <- vector(length = seq_length)

    fibo_seq[1:2] <- c(first_num, second_num)

    for(i in 3:seq_length){
      fibo_seq[i] <- fibo_seq[i - 2] + fibo_seq[i - 1]
    }

    fibo_seq

  }

}