R/crm_extract.R

In ropenscilabs/crminer: Fetch 'Scholary' Full Text from 'Crossref'

#' Extract text from a single pdf document
#'
#' @export
#' @param path (character) path to a file, file must exist
#' @param raw (raw) raw bytes
#' @param try_ocr (logical) whether to try extracting OCRed 
#' pages with `pdftools::pdf_ocr_text()`. default: `FALSE`.
#' if `FALSE`, we use `pdftools::pdf_text()`
#' @param ... args passed on to `pdftools::pdf_info()`
#' and `pdftools::pdf_text()` (or `pdftools::pdf_ocr_text()` if
#' `try_ocr=TRUE`) - any args are passed to
#' both of those function calls, which makes sense
#' @return An object of class `crm_pdf` with a slot for
#' `info` (pdf metadata essentially), and `text` (the extracted
#' text) - with an attribute (`path`) with the path to the pdf
#' on disk
#' @details We use \pkg{pdftools} under the hood to do pdf text
#' extraction. 
#' 
#' You have to supply either `path` or `raw` - not both.
#' @examples
#' path <- system.file("examples", "MairChamberlain2014RJournal.pdf",
#'    package = "crminer")
#' (res <- crm_extract(path))
#' res$info
#' res$text
#' # with newlines, pretty print
#' cat(res$text)
#'
#' # another example
#' path <- system.file("examples", "ChamberlainEtal2013Ecosphere.pdf",
#'    package = "crminer")
#' (res <- crm_extract(path))
#' res$info
#' cat(res$text)
#' 
#' # with raw pdf bytes
#' path <- system.file("examples", "raw-example.rds", package = "crminer")
#' rds <- readRDS(path)
#' class(rds)
#' crm_extract(raw = rds)
crm_extract <- function(path = NULL, raw = NULL, try_ocr = FALSE, ...) {
  assert(try_ocr, "logical")
  stopifnot(xor(is.null(path), is.null(raw)))
  if (!is.null(path)) {
    path <- path.expand(path)
    if (!file.exists(path)) stop("path does not exist", call. = FALSE)  
  } else {
    assert(raw, "raw")
    path <- raw
  }
  fun <- if (try_ocr) pdftools::pdf_ocr_text else pdftools::pdf_text
  
  structure(
    list(
      info = pdftools::pdf_info(path, ...),
      text = fun(path, ...)
    ),
    class = "crm_pdf",
    path = if (is.character(path)) path else 'raw'
  )
}

#' @export
print.crm_pdf <- function(x, ...) {
  cat("<document>", attr(x, "path"), "\n", sep = "")
  cat("  Pages: ", x$info$pages, "\n", sep = "")
  cat("  No. characters: ", sum(nchar(x$text)), "\n", sep = "")
  cat("  Created: ", as.character(as.Date(x$info$created)), "\n",
      sep = "")
}
#' @export
print.crm_pdf_text <- function(x, ...) {
  cat("<document>", attr(x, "path"), "\n", sep = "")
  cat("  No. characters: ", sum(nchar(x$text)), "\n", sep = "")
}