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extract_areas

Source: R/locate_area.R
extract_areas.Rd

Interactively identify areas and extract

Usage

locate_areas(
  file,
  pages = NULL,
  thumbnails = NULL,
  resolution = 60L,
  widget = c("shiny", "native", "reduced"),
  copy = FALSE
)

extract_areas(file, pages = NULL, guess = FALSE, copy = FALSE, ...)

Arguments

file

A character string specifying the path to a PDF file. This can also be a URL, in which case the file will be downloaded to the R temporary directory using download.file.

pages

An optional integer vector specifying pages to extract from. To extract multiple tables from a given page, repeat the page number (e.g., c(1,2,2,3)).

thumbnails

A directory containing prefetched thumbnails created with the function make_thumbnails. This will greatly increase loading speed.

resolution

An integer specifying the resolution of the PNG images conversions. A low resolution is used by default to speed image loading.

widget

A one-element character vector specifying the type of “widget” to use for locating the areas. The default (“shiny”) is a shiny widget. The alternatives are a widget based on the native R graphics device (“native”, where available), or a very reduced functionality model (“reduced”).

copy

Specifies whether the original local file(s) should be copied to tempdir() before processing. FALSE by default. The argument is ignored if file is URL.

guess

See extract_tables (note the different default value).

...

Other arguments passed to extract_tables.

Value

For extract_areas, see extract_tables. For locate_areas, a list of four-element numeric vectors (top,left,bottom,right), one per page of the file.

Details

extract_areas is an interactive mode for extract_tables allowing the user to specify areas of each PDF page in a file that they would like extracted. When used, each page is rendered to a PNG file and displayed in an R graphics window sequentially, pausing on each page to call locator so the user can click and highlight an area to extract.

The exact behaviour is a somewhat platform-dependent, and depends on the value of widget (and further, whether you are working in RStudio or the R console). In RStudio (where widget = "shiny"), a Shiny gadget is provided which allows the user to click and drag to select areas on each page of a file, clicking “Done” on each page to advance through them. It is not possible to return to previous pages. In the R console, a Shiny app will be launched in a web browser.

For other values of widget, functionality is provided through the graphics device. If graphics events are supported, then it is possibly to interactively highlight a page region, make changes to that region, and navigate through the pages of the document while retaining the area highlighted on each page. If graphics events are not supported, then some of this functionality is not available (see below).

In full functionality mode (widget = "native"), areas are input in a native graphics device. For each page, the first mouse click on a page initializes a highlighting rectangle; the second click confirms it. If unsatisfied with the selection, the process can be repeated. The window also responds to keystrokes. PgDn, Right, and Down advance to the next page image, while PgUp, Left, and Up return to the previous page image. Home returns to the first page image and End advances to the final page image. Q quits the interactive mode and proceeds with extraction. When navigating between pages, any selected areas will be displayed and can be edited. Delete removes a highlighted area from a page (and then displays it again). (This mode may not work correctly from within RStudio.)

In reduced functionality mode (where widget = "reduced" or on platforms where graphics events are unavailable), the interface requires users to indicate the upper-left and lower-right (or upper-right and lower-left) corners of an area on each page, this area will be briefly confirmed with a highlighted rectangle and the next page will be displayed. Dynamic page navigation and area editing are not possible.

In any of these modes, after the areas are selected, extract_areas passes these user-defined areas to extract_tables. locate_areas implements the interactive component only, without actually extracting; this might be useful for interactive work that needs some modification before executing extract_tables computationally.

See also

extract_tables, make_thumbnails, , get_page_dims

Author

Thomas J. Leeper <thosjleeper@gmail.com>

Examples

if (interactive()) {
  # simple demo file
  f <- system.file("examples", "mtcars.pdf", package = "tabulapdf")

  # locate areas only, using Shiny app
  locate_areas(f)

  # locate areas only, using native graphics device
  locate_areas(f, widget = "shiny")

  # locate areas and extract
  extract_areas(f)
}