Jeroen Ooms

A new version of pdftools has been released to CRAN. Go get it while
it's hot:

::: {.highlight}
``` {.chroma tabindex="0"}
install.packages("pdftools")
```
:::

This version has two major improvements: low level text extraction and
encoding improvements.

## About PDF textboxes

A pdf document may seem to contain paragraphs or tables in a viewer, but
this is not actually true. PDF is a *printing format*: a page consists
of a series of unrelated lines, bitmaps, and textboxes with a given
size, position and content. Hence a table in a pdf file is really just a
large unordered set of lines and words that are nicely visually
positioned. This makes sense for printing, but makes extracting text or
data from a pdf file extremely difficult.

Because the pdf format has little semantic structure, the `pdf_text()`
function in pdftools has to render the PDF to a text canvas, in order to
create the sentences or paragraphs. It does so pretty well, but some
users have asked for something more low level.

> [@opencpu](https://twitter.com/opencpu?ref_src=twsrc%5Etfw) any chance
> pdftext could return a data frame with one row for each text box with
> columns giving page, positions, and contents?
>
> --- Hadley Wickham (@hadleywickham) [December 26,
> 2017](https://twitter.com/hadleywickham/status/945729495956369409?ref_src=twsrc%5Etfw)

Unfortunately this was not trivial because it required some work in the
underlying [poppler](https://poppler.freedesktop.org/) library. One year
later, and this functionality is now finally available in the upcoming
poppler version 0.73. The pdftools [CRAN binary
packages](https://cran.r-project.org/package=pdftools) for Windows and
MacOS already contain a suitable libpoppler, however Linux users
probably have to wait for the latest version of poppler to become
available in their system package manager (or [compile from
source](https://github.com/ropensci/pdftools#on-ubuntu)).

## Low-level text extraction

We use an [example pdf
file](https://github.com/ropensci/tabulizer/raw/master/inst/examples/data.pdf)
from the rOpenSci tabulizer package. This file contains a few standard
datasets which have been printed as a pdf table. First let's try the
`pdf_text()` function, which returns a character vector of length equal
to the number of pages in the file.

::: {.highlight}
``` {.chroma tabindex="0"}
library(pdftools)pdf_file <- "https://github.com/ropensci/tabulizer/raw/master/inst/examples/data.pdf"txt <- pdf_text(pdf_file)cat(txt[1])
```
:::

``` {tabindex="0"}
                    mpg  cyl    disp  hp drat    wt  qsec vs am gear carbMazda RX4           21.0   6   160.0 110 3.90 2.620 16.46  0  1    4    4Mazda RX4 Wag       21.0   6   160.0 110 3.90 2.875 17.02  0  1    4    4Datsun 710          22.8   4   108.0  93 3.85 2.320 18.61  1  1    4    1Hornet 4 Drive      21.4   6   258.0 110 3.08 3.215 19.44  1  0    3    1Hornet Sportabout   18.7   8   360.0 175 3.15 3.440 17.02  0  0    3    2Valiant             18.1   6   225.0 105 2.76 3.460 20.22  1  0    3    1Duster 360          14.3   8   360.0 245 3.21 3.570 15.84  0  0    3    4Merc 240D           24.4   4   146.7  62 3.69 3.190 20.00  1  0    4    2...
```

Hence `pdf_text()` converts all text on a page to a large string, which
works pretty well. However if you would want to parse this text into a
data frame (using e.g. `read.table`) you run into a problem: the first
column contains spaces within the values. Therefore we can't use the
whitespace as the column delimiter (as is the default in `read.table`).

Hence to write a proper pdf table extractor, we have to infer the column
from the *physical position* of the textbox, rather than rely on
delimiting characters. The new `pdf_data()` provides exactly this. It
returns a data frame with all textboxes in a page, including their
width, height, and (x,y) position:

::: {.highlight}
``` {.chroma tabindex="0"}
# All textboxes on page 1pdf_data(pdf_file)[[1]]
```
:::

``` {tabindex="0"}
# A tibble: 430 x 6   width height     x     y space text     <int>  <int> <int> <int> <lgl> <chr>  1    29      8   154   139 TRUE  Mazda  2    19      8   187   139 FALSE RX4    3    29      8   154   151 TRUE  Mazda  4    19      8   187   151 TRUE  RX4    5    19      8   210   151 FALSE Wag    6    31      8   154   163 TRUE  Datsun 7    14      8   189   163 FALSE 710    8    30      8   154   176 TRUE  Hornet 9     4      8   188   176 TRUE  4     10    23      8   196   176 FALSE Drive 
```

Converting this pdf data into the original data frame is left as an
exercise for the reader :)

## Encoding enhancements

Apart from the new `pdf_data()` function, this release also fixes a few
smaller problems related to text encoding, both in pdftools package as
well as the underlying poppler library. The main issue was a bug related
mixing `UTF-16BE` and `UTF-16LE`, which is not something you ever want
to worry about.

For most well behaved pdf files there was no problem, but some files
using rare encoding could yield an error `Embedded NUL in string` for
metadata, or garbled `author` or `title` fields. If you encountered any
of these problems in the past, please update your `pdftools` and try
again!

## Other rOpenSci PDF packages

Besides `pdftools` we have two other packages that may be helpful to
extract data from PDF files:

- The
  [tesseract](https://cran.r-project.org/web/packages/tesseract/vignettes/intro.html)
  package provides R bindings to the Google Tesseract OCR C++ library.
  This allows for detecting text from scanned images.
- The
  [tabulizer](https://cran.r-project.org/web/packages/tabulizer/vignettes/tabulizer.html)
  package provides R bindings to the [Tabula java
  library](https://github.com/tabulapdf/tabula-java/), which can also be
  used to extract tables from PDF documents. Note this requires you have
  a Java installation.

Using rOpenSci packages? Tell us about your [use
case](https://discuss.ropensci.org/c/usecases) and how you make use of
our software!


A new version of pdftools has been released to CRAN. Go get it while it’s hot:install.packages("pdftools") This version has two major improvements: low level text extraction and encoding improvements.About PDF textboxes  A pdf document may seem to contain paragraphs or tables in a viewer, but this is not actually true.

Postagens de Rogue Scholar

Pdftools 2.0: powerful pdf text extraction tools