fugly

This package provides a single function (str_capture) for using named capture groups to extract values from strings. A key requirement for readability is that the names of the capture groups are specified inline as part of the regex, and not in an external vector or as separate names.

fugly::str_capture() is implemented as a wrapper around stringr. This is because stringr itself does not yet do named capture groups (See issues for stringr and stringi).

fugly::str_capture() is very similar to a number of existing packages. See table below for a comparison.

What do I mean when I say fugly::str_capture() is unsafe/dodgy/non-robust?

• It doesn’t adhere to standard regular expression syntax for named capture groups as used in perl, python etc.

• It doesn’t really adhere to glue syntax (although it looks similar at a surface level).

• If you specify delimiters which appear in your string input, then you’re going to have a bad time.

• It’s generally only been tested on data which is:

  • highly structured
  • only ASCII
  • non-pathological

What’s in the box?

• fugly::str_capture(string, pattern, delim)

  • capture named groups with regular expressions
  • returns a data.frame with all columns containing character strings
  • can mix-and-match with non-capturing regular expressions
  • if no regular expression specified for a named group then .*? is used.
  • does not do any type guessing/conversion.

Installation

You can install from GitHub with:

# install.package('remotes')
remotes::install_github('coolbutuseless/fugly')

Example 1

In the following example:

• Input consists of multiple strings
• capture groups are delimited by {} by default.
• the regex for the capture group for name is unspecified, so .*? will be used
• the regex for the capture group for age is \d+ i.e. match must consist of 1-or-more digits

library(fugly)

string <- c(
  "information: Name:greg Age:27 ",
  "information: Name:mary Age:34 "
)

str_capture(string, pattern = "Name:{name} Age:{age=\\d+}")

#>   name age
#> 1 greg  27
#> 2 mary  34

Example 2

A more complicated example:

• Note the mixture of capturing groups and a bare .*? in the pattern which is not returned as a result

string <- c(
'{"type":"Feature","properties":{"hash":"1348778913c0224a","number":"27","street":"BANAMBILA STREET","unit":"","city":"ARANDA","district":"","region":"ACT","postcode":"2614","id":"GAACT714851647"},"geometry":{"type":"Point","coordinates":[149.0826143,-35.2545558]}}',
'{"type":"Feature","properties":{"hash":"dc776871c868bc7e","number":"139","street":"BOUVERIE STREET","unit":"UNIT 711","city":"CARLTON","district":"","region":"VIC","postcode":"3053","id":"GAVIC423944917"},"geometry":{"type":"Point","coordinates":[144.9617149,-37.8032551]}}',
'{"type":"Feature","properties":{"hash":"8197f34a40ccad47","number":"6","street":"MOGRIDGE STREET","unit":"","city":"WARWICK","district":"","region":"QLD","postcode":"4370","id":"GAQLD155949502"},"geometry":{"type":"Point","coordinates":[152.0230999,-28.2230133]}}',
'{"type":"Feature","properties":{"hash":"18edc96308fc1a8e","number":"22","street":"ORR STREET","unit":"UNIT 507","city":"CARLTON","district":"","region":"VIC","postcode":"3053","id":"GAVIC424282716"},"geometry":{"type":"Point","coordinates":[144.9653484,-37.8063371]}}'
)


str_capture(string, pattern = '"number":"{number}","street":"{street}".*?"coordinates":\\[{coords}\\]')

#>   number           street                  coords
#> 1     27 BANAMBILA STREET 149.0826143,-35.2545558
#> 2    139  BOUVERIE STREET 144.9617149,-37.8032551
#> 3      6  MOGRIDGE STREET 152.0230999,-28.2230133
#> 4     22       ORR STREET 144.9653484,-37.8063371

Simple Benchmark

I acknowledge that this isn’t the greatest benchmark, but it is relevant to my current use-case.

• nc with the PCRE regex engine is the fastest named capture I could find in R.

  • However - I’m not a huge fan of its syntax

• For large inputs (1000+ input strings), fugly is significantly faster than unglue, utils::strcapture and ``ore`

• The rust regex engine rr4r is slightly faster than fugly

• unglue is the slowest of the methods.

• ore lies somewhere between unglue and utils::strcapture

• As pointed out by Michael Barrowman, tidyr::extract() will also do named capture into a data.frame.

  • Similar to utils::strcapture(), the names are not specified inline with the regex, but are listed separately.

# remotes::install_github("jonclayden/ore")
# remotes::install_github("yutannihilation/rr4r")
# remotes::install_github('qinwf/re2r') 
library(ore)
library(rr4r)
library(unglue)
library(ggplot2)
library(tidyr)

# meaningless strings for benchmarking
N <- 1000
string <- paste0("Information name:greg age:", seq(N))


res <- bench::mark(
  `fugly::str_capture()` = fugly::str_capture(string, "name:{name} age:{age=\\d+}"),
  `unglue::unglue()` = unglue::unglue_data(string, "Information name:{name} age:{age=\\d+}"),
  `utils::strcapture()` = utils::strcapture("Information name:(.*?) age:(\\d+)", string, 
                    proto = data.frame(name=character(), age=character())),
  `ore::ore_search()` = do.call(rbind.data.frame, lapply(ore_search(ore('name:(?<name>.*?) age:(?<age>\\d+)', encoding='utf8'), string, all=TRUE), function(x) {x$groups$matches})),
   `rr4r::rr4r_extract_groups()` = rr4r::rr4r_extract_groups(string, "name:(?P<name>.*?) age:(?P<age>\\d+)"),
  `nc::capture_first_vec() PCRE` = nc::capture_first_vec(string, "Information name:", name=".*?", " age:", age="\\d+", engine = 'PCRE'),
  `tidyr::extract()` = tidyr::extract(data.frame(x = string), x, into = c('name', 'age'), regex = 'name:(.*?) age:(\\d+)'),
  check = FALSE
)

Related Software

• stringr
• utils::strcapture()
• unglue::unglue()
• ore, ore on CRAN
• namedCapture Note: I couldn’t get this to work sanely.
• rr4f rust regex engine
• nc

Acknowledgements

• R Core for developing and maintaining the language.
• CRAN maintainers, for patiently shepherding packages onto CRAN and maintaining the repository