R/get_learning_obj.R

In jhudsl/cow: Course Organizer and Wrangler

#' Retrieve learning objectives for a chapter
#'
#' Given an repository on GitHub, retrieve all the bookdown chapter
#' information for the Github page if it exists.
#' Currently only public repositories are supported.
#'
#' @param url a url to a bookdown chapter
#' e.g. "https://jhudatascience.org/Documentation_and_Usability/what-does-good-documentation-look-like.html"
#' @param prompt A string character that is a prompt lead in to the Learning objectives and should be deleted.
#'
#' @return find learning objectives for a particular chapter
#'
#' @importFrom magrittr %>%
#' @import dplyr
#'
#' @export
#'
#' @examples \dontrun{
#'
#' # Declare chapter URL
#' url <- "https://jhudatascience.org/Documentation_and_Usability/other-helpful-features.html"
#'
#' get_learning_obj(url)
#' }
get_learning_obj <- function(url, prompt = "This chapter will demonstrate how to\\:") {

  # Try chapter url
  chapt_html <- suppressWarnings(try(xml2::read_html(paste(url, collapse = "\n"))))

  # Extract chapter nodes
  nodes <- rvest::html_nodes(chapt_html, xpath = paste0("//", "img"))

  # Get alternative text
  fig_alts <- rvest::html_attr(nodes, "alt")

  # Get learning objectives from alternative text from images
  learning_objs <- grep("learning objective", fig_alts, ignore.case = TRUE, value = TRUE)

  # Get rid of "learning objectives" bit
  learning_objs <- gsub("learning objectives?", "", learning_objs, ignore.case = TRUE)

  # Get rid of "learning objectives" bit
  learning_objs <- gsub(prompt, "", learning_objs, ignore.case = TRUE)

  # Trim white space and weird periods
  learning_objs <- trimws(learning_objs)
  learning_objs <- trimws(gsub("^\\.", "", learning_objs))

  # Make it an NA if its blank
  learning_objs <- ifelse(length(learning_objs) == 0, NA, learning_objs)

  return(learning_objs)
}