R/OEIS_example.R

In EnriquePH/OEIS.R: Data from the on-Line Encyclopedia of Integer Sequences in R

#  ----------------------------------------------------------------------------
#  OEIS.R PACKAGE
#  Data from The On-Line Encyclopedia of Integer Sequences in R
#  File: OEIS_example.R
#  (c) 2017 - Enrique Pérez Herrero
#  email: eph.project1500@gmail.com
#  GNU GENERAL PUBLIC LICENSE Version 3, 29 June 2007
#  ---------------------------------------------------------------------------

#  OEIS_example
#' OEIS sequence example lines from sequence \code{internal_format}
#'
#' These lines give expanded information or examples to illustrate the initial
#' terms of the sequence.
#' @inheritParams OEIS_description
#'
#' @importFrom magrittr "%>%"
#'
#' @seealso * \code{\link{OEIS_description}}
#' @seealso * \code{\link{OEIS_author}}
#' @seealso * \code{\link{OEIS_internal_format}}
#' @seealso * \code{\link{OEIS_formula}}
#' @seealso * \code{\link{OEIS_sequence}}
#' @seealso * \code{\link{OEIS_xml}}
#' @return A character string with the OEIS sequence lines of examples or
#'   \code{NULL} where no examples are available.
#'
#' @examples
#' id <- "A105805"
#' internal_format <- OEIS_internal_format(id)
#' example <- OEIS_example(internal_format)
#' cat(example, sep = "\n")
#'
#' @export
OEIS_example <- function(x) {
  UseMethod("OEIS_example", x)
}

#' @method OEIS_example character
#' @export
OEIS_example.character <- function(x) {
  OEIS_check(x) %>%
    OEIS_example
}

#' @method OEIS_example OEIS_ID
#' @export
OEIS_example.OEIS_ID <- function(x) {
  x %>%
    OEIS_internal_format %>%
    OEIS_example %>%
    char0toNULL
}

#' @method OEIS_example OEIS_internal
#' @export
OEIS_example.OEIS_internal <- function(x) {
  . <- NULL
  x[x$tag == "%e", ]$line %>%
    gsub("_", "", .) %>%
    sapply(., trimws, USE.NAMES = FALSE) %>%
    char0toNULL
}

#' @method OEIS_example OEIS_xml
#' @export
OEIS_example.OEIS_xml <- function(x) {
  . <- NULL
  example <- x %>%
    OEIS_df %>%
    .[.$Line == "EXAMPLE", ] %>%
    .$Description
  if (identical(example, character(0))) {
    example <- NULL
  } else {
    example %<>%
      strsplit(., "\n") %>%
      sapply(., trimws) %>%
      .[. != "", ]
  }
  example
}

#' @method OEIS_example OEIS_sequence
#' @export
OEIS_example.OEIS_sequence <- function(x) {
  x$example
}