# ----------------------------------------------------------------------------
# OEIS.R PACKAGE
# Data from The On-Line Encyclopedia of Integer Sequences in R
# File: OEIS_example.R
# (c) 2017 - Enrique PĂ©rez 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
}
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