R/extract_text.R

In leeper/tabulizer: Extract tables from PDF documents

#' @title extract_text
#' @description Extract text from a file
#' @param file A character string specifying the path or URL to a PDF file.
#' @param pages An optional integer vector specifying pages to extract from.
#' @param area An optional list, of length equal to the number of pages specified, where each entry contains a four-element numeric vector of coordinates (top,left,bottom,right) containing the table for the corresponding page. As a convenience, a list of length 1 can be used to extract the same area from all (specified) pages.
#' @param password Optionally, a character string containing a user password to access a secured PDF.
#' @param encoding Optionally, a character string specifying an encoding for the text, to be passed to the assignment method of \code{\link[base]{Encoding}}.
#' @param copy Specifies whether the original local file(s) should be copied to
#' \code{tempdir()} before processing. \code{FALSE} by default. The argument is
#' ignored if \code{file} is URL.
#' @details This function converts the contents of a PDF file into a single unstructured character string.
#' @return If \code{pages = NULL} (the default), a length 1 character vector, otherwise a vector of length \code{length(pages)}.
#' @author Thomas J. Leeper <thosjleeper@gmail.com>
#' @examples
#' \dontrun{
#' # simple demo file
#' f <- system.file("examples", "text.pdf", package = "tabulapdf")
#'
#' # extract all text
#' extract_text(f)
#'
#' # extract all text from page 1 only
#' extract_text(f, pages = 1)
#'
#' # extract text from selected area only
#' extract_text(f, area = list(c(209.4, 140.5, 304.2, 500.8)))
#' }
#' @seealso \code{\link{extract_tables}}, \code{\link{extract_areas}}, \code{\link{split_pdf}}
#' @importFrom rJava J new
#' @export
extract_text <- function(file,
                         pages = NULL,
                         area = NULL,
                         password = NULL,
                         encoding = NULL,
                         copy = FALSE) {
  pdfDocument <- load_doc(file, password = password, copy = copy)
  on.exit(pdfDocument$close())

  if (!is.null(pages)) {
    tryCatch(pages <- as.integer(pages),
      error = function(e) {
        stop("'pages' should be an integer or coercible to integer.")
      }
    )
  }

  if (!is.null(area)) {
    stripper <- new(J("org.apache.pdfbox.text.PDFTextStripperByArea"))
  } else {
    stripper <- new(J("org.apache.pdfbox.text.PDFTextStripper"))
  }

  if (!is.null(area)) {
    npages <- pdfDocument$getNumberOfPages()
    area <- make_area(area = area, pages = pages, npages = npages, target = "java")
    if (!is.null(pages)) {
      pageIndex <- pages - 1L
    } else {
      pageIndex <- seq_len(npages) - 1L
    }
    out <- unlist(Map(function(x, y) {
      PDPage <- pdfDocument$getPage(x)
      region <- "text"
      stripper$removeRegion(region)
      stripper$addRegion(region, y)
      stripper$extractRegions(PDPage)
      stripper$getTextForRegion(region)
    }, pageIndex, area))
  } else if (!is.null(pages) && is.null(area)) {
    out <- unlist(lapply(pages, function(x) {
      stripper$setStartPage(x)
      stripper$setEndPage(x)
      stripper$getText(pdfDocument)
    }))
  } else {
    out <- stripper$getText(pdfDocument)
  }

  if (!is.null(encoding)) {
    Encoding(out) <- encoding
  }
  out
}