Regular Expressions in R Programming Language

# R offers built-in support for regular expressions.
# Here are some examples of common regexp-related tasks in R.

# This tests whether a pattern matches a string.
match <- grepl("p([a-z]+)ch", "peach")
print(match)

# For other regexp tasks, we'll use the stringr package
# which provides a consistent interface for working with regular expressions.
library(stringr)

# Create a regular expression pattern
r <- "p([a-z]+)ch"

# Test if the pattern matches a string
print(str_detect("peach", r))

# Find the first match for the regexp
print(str_extract("peach punch", r))

# Find the start and end indexes for the match
print(str_locate("peach punch", r))

# Extract both the whole-pattern matches and the submatches
print(str_match("peach punch", r))

# Find all matches for a regexp
print(str_extract_all("peach punch pinch", r))

# Replace subsets of strings with other values
print(str_replace("a peach", r, "<fruit>"))

# Transform matched text with a given function
print(str_replace_all("a peach", r, toupper))

# Compile a regular expression for repeated use
r_compiled <- str_c("p([a-z]+)ch")
print(r_compiled)

# Use the compiled regexp
print(str_extract_all("peach punch pinch", r_compiled))

This R code demonstrates various regular expression operations using both base R functions and the stringr package, which provides a more consistent interface for working with regular expressions in R.

Here’s a breakdown of the operations:

1. We use grepl() from base R to test if a pattern matches a string.

2. We load the stringr package for more advanced regex operations.

3. str_detect() is used to test if a pattern matches a string.

4. str_extract() finds and returns the first match for the regexp.

5. str_locate() returns the start and end indexes of the first match.

6. str_match() extracts both the whole-pattern matches and submatches.

7. str_extract_all() finds all matches for a regexp.

8. str_replace() replaces subsets of strings with other values.

9. str_replace_all() with a function argument transforms matched text.

10. We use str_c() to create a compiled regular expression pattern.

Note that R doesn’t have a direct equivalent to Go’s regexp.Compile() or regexp.MustCompile(). In R, regular expressions are typically used directly as strings, and any “compilation” is handled internally by the functions that use them.

To run this R script, save it to a file (e.g., regular_expressions.R) and run it using:

$ Rscript regular_expressions.R

For a complete reference on R regular expressions, check the documentation for the stringr package and the base R regex functions (?regex in R).