Regular expression basics

Introduction to Natural Language Processing in R

Kasey Jones

Research Data Scientist

What is natural language processing?

NLP:

Topics Covered:

A sequence of characters used to search text
Examples include:
- searching files in a directory using the command line
- finding articles that contain a specific pattern
- replacing specific text
- ...

words <- c("DW-40", "Mike's Oil", "5w30", "Joe's Gas", "Unleaded", "Plus-89")

# Finding Digits
grep("\\d", words, value = TRUE)

[1] 1 3 6

# Finding Apostrophes
grep("\\'", words, value = TRUE)

[1] "Mike's Oil"     "Joe's Gasoline"

Pattern	Text Matches	R Example	Text Example
\w	Any alphanumeric	gregexpr(pattern ='\w', <text>)	a
\d	Any digit	gregexpr(pattern ='\d', text)	1
\w+	An alphanumeric of any length	gregexpr(pattern ='\w+', text)	word
\d+	Digits of any length	gregexpr(pattern ='\d+', text)	1234
\s	Spaces	gregexpr(pattern ='\s', text)	' '
\S	Any non-space	gregexpr(pattern ='\S', text)	word

Function	Purpose	Syntax
grep	Find matches of the pattern in a vector	grep(pattern ='\w', x = <vector>, value = F)
gsub	Replaces all matches of a string/vector	gsub(pattern ='\d+', replacement = "", x = <vector>)

There are several online resources for practicing regular expressions. These resources go into great detail and provide a wide range of examples.

¹ https://regexone.com/lesson/matching_characters

Introduction to Natural Language Processing in R