In moodymudskipper/unglue: Extract Matched Substrings Using a Pattern

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unglue

The package unglue features functions such as unglue(), unglue_data() and unglue_unnest() which provide in many cases a more readable alternative to base regex functions. Simple cases indeed don't require regex knowledge at all.

It uses a syntax inspired from the functions of Jim Hester's glue package to extract matched substrings using a pattern, but is not endorsed by the authors of glue nor tidyverse packages.

It is completely dependency free, though formula notation of functions is supported if rlang is installed.

Installation:

# CRAN version:
install.packages("unglue")
# Development version:
remotes::install_github("moodymudskipper/unglue")

using an example from ?glue::glue backwards

library(unglue)
library(glue)
library(magrittr)
library(utils)
glued_data <- head(mtcars) %>% glue_data("{rownames(.)} has {hp} hp")
glued_data
unglue_data(glued_data, "{rownames(.)} has {hp} hp")

use several patterns, the first that matches will be used

facts <- c("Antarctica is the largest desert in the world!",
"The largest country in Europe is Russia!",
"The smallest country in Europe is Vatican!",
"Disneyland is the most visited place in Europe! Disneyland is in Paris!",
"The largest island in the world is Green Land!")
facts_df <- data.frame(id = 1:5, facts)

patterns <- c("The {adjective} {place_type} in {bigger_place} is {place}!",
            "{place} is the {adjective} {place_type=[^ ]+} in {bigger_place}!{=.*}")
unglue_data(facts, patterns)

Note that the second pattern uses some regex, regex needs to be typed after an = sign, if its has no left hand side then the expression won't be attributed to a variable. in fact the pattern "{foo}" is a shorthand for "{foo=.*?}".

escaping characters

Special characters outside of the curly braces should not be escaped.

sentences <- c("666 is [a number]", "foo is [a word]", "42 is [the answer]", "Area 51 is [unmatched]")
patterns2 <- c("{number=\\d+} is [{what}]", "{word=\\D+} is [{what}]")
unglue_data(sentences, patterns2)

type conversion

In order to convert types automatically we can set convert = TRUE, in the example above the column number will be converted to numeric.

unglue_data(sentences, patterns2, convert = TRUE)

convert = TRUE triggers the use of utils::type.convert with parameter as.is = TRUE. We can also set convert to another conversion function such as readr::type_convert, or to a formula is rlang is installed.

unglue_unnest()

unglue_unnest() is named as a tribute to tidyr::unnest() as it's equivalent to using successively unglue() and unnest() on a data frame column. It is similar to tidyr::extract() in its syntax and efforts were made to make it as consistent as possible.

unglue_unnest(facts_df, facts, patterns)
unglue_unnest(facts_df, facts, patterns, remove = FALSE)

unglue_vec()

While unglue() returns a list of data frames, unglue_vec() returns a character vector (unless convert = TRUE), if several matches are found in a string the extracted match will be chosen by name or by position.

unglue_vec(sentences, patterns2, "number")
unglue_vec(sentences, patterns2, 1)

unglue_detect()

unglue_detect() returns a logical vector, it's convenient to check that the input was matched by a pattern, or to subset the input to take a look at unmatched elements.

unglue_detect(sentences, patterns2)
subset(sentences, !unglue_detect(sentences, patterns2))

unglue_regex()

unglue_regex() returns a character vector of regex patterns, all over functions are wrapped around it and it can be used to leverage the unglue in other functions.

unglue_regex(patterns)
unglue_regex(patterns, named_capture = TRUE)
unglue_regex(patterns, attributes = TRUE)

unglue_sub()

unglue_sub() substitute substrings using strings or replacement functions

unglue_sub(
  c("a and b", "foo or BAR"),
  c("{x} and {y}", "{x} or {z}"),
  list(x= "XXX", y = toupper, z = ~tolower(.)))

duplicated labels

We can ensure that a pattern is repeated by repeating its label

unglue_data(c("black is black","black is dark"), "{color} is {color}")

We can change this behavior by feeding a function to the multiple parameter, in that case this function will be applied on the matches.

unglue_data(c("System: Windows, Version: 10","System: Ubuntu, Version: 18"), 
            "System: {OS}, Version: {OS}", multiple = paste)

moodymudskipper/unglue documentation built on Dec. 8, 2024, 9:07 p.m.