Regular Expression (REGEX) in R

In computing, a regular expression (abbreviated regexp) is a sequence of characters that forms a search pattern, mainly for use in pattern matching with strings. The patterns are often a combination of text abbreviations, meta characters, and wild cards. Regular expressions are used for searching for objects, doing extractions, or find/replace operations. The use of regular expressions offers convenience and can have powerful impact on data or object management.

Functions in R

Functions in R for regular expressions include:

Function Description
grep(regexp, vector) Finds all the strings in the vector that contain a substring match regexp
sub(regexp, replacement, vector) Replaces the first substring matching the regular expression with the replacement (for each element of the vector).
gsub() Does the same thing as sub() but can make more than one replacement per string.
regexpr(regexp, vector) Returns the position of the first match within each string.
gregexpr() Is the same as regexpr() except that it returns all matches.
strsplit() Splits a string at each match to a regular expression
glob2rx() Converts filename wildcard specifications to regular expressions.

Basic Pattern Concepts

A pattern is an expression used to specify a set of strings required for a particular purpose. A simple way to specify a set of strings is complete enumeration, or simply listing all elements or members. However, there are more concise ways to specify the desired set of strings. For example, the set containing the three strings “Handel”, “Händel”, and “Haendel” can be specified by the pattern H(ä|ae?)ndel. This pattern matches each of the three strings. If there exists at least one regexp that matches a particular set then there exists at least another pattern, and possibly an infinite number of patterns, that generate the same result.

Pattern matching frequently makes use of the following operations to construct regular expressions.

Boolean “or”

A vertical bar separates alternatives. For example, gray|grey can match “gray” or “grey”.


Parenthesis define the scope and precedence of the operators. For example, gray|grey and gr(a|e)y are equivalent patterns which both describe the set of “gray” or “grey”.


A quantifier after a token (such as a character) or group specifies how often that element is allowed to occur. The most common quantifiers are the question mark ?, the asterisk *, and the plus sign +.

For example:

? The question mark indicates that there is 0 or 1 of the preceding elements. Hence, colou?r is a pattern that matches both color and colour;

* The asterisk is a well known wild card that indicates there is 0 or more of the preceding elements. Hence, ab*c matches ac, abc, abbc, abbbc, and so on; and

+ The plus sign indicates there is one or more of the preceding elements. Thus, ab+c matches abc, abbc, abbbc, and so on, but not ac.

These constructions can be combined to form arbitrarily complex expressions, much like one can constructs arithmetical expressions from numbers. For example, H(ae?|ä)ndel and H(a|ae|ä)ndel are both valid patterns which match the same strings as the earlier example, H(ä|ae?)ndel.


Sabalico Logo
Sabali Mail Logo
Domain Search Logo
Test Speed Logo
Website On Logo
Page Load Logo
Code Editor Logo
Format Code Logo
HTML Validator Logo
CSS Validator Logo
ASCII Table Logo
HTML Symbols Logo
Emoji Symbols Logo
Encode File Logo
Sitemap Generator Logo
Generator Password Logo
QR Code Generator Logo
Barcode Generator Logo
Online Sign Logo
Dictionary Online Logo
Counter Word Logo
Text Convert Logo
Lorem Ipsum Generator Logo
Sprite Sheet Logo
Edit Picture Logo
Resize Image Logo
Image Compress Logo
Image Color Logo
Image Crop Logo
Combine Images Logo
Favicon Generator Logo
Color Palette Logo
Color Picker Logo
Color Mix Logo
Color Convert Logo
CSS Gradient Logo
To-Do List Logo
Calendar Free Logo
Generator Meme Logo
Word Spinner Logo
Phone Country Logo
Sabalytics Logo
Senty Logo
World Map Logo
SEO Guide Logo
Keyword Tool Logo
What is my IP Logo
My Device Logo
My Browser Logo
My Location Logo
Time Zone Logo
Day Map Logo
My Weather Logo
My Galaxy Logo
The Moon Logo
Periodic Table Logo
rStatistics Logo
Unit Convert Logo
Data Convert Logo
Coordinate Converter Logo
Temperature Convert Logo
2020 Election Logo
Sabali Finance Logo
Currency Convert Logo
Free Calculator Logo
Finance Calculator Logo
Loan Calculator Logo
Calculator Mortgage Logo
Stock Calculator Logo
Bond Calculator Logo
Tax Calculator Logo
Tip Calculator Logo
Gas Mileage Logo
History of Humanity - History Archive Logo
History of Humanity - History Mysteries Logo
History of Humanity - Ancient Mesopotamia Logo
History of Humanity - Egypt History Logo
History of Humanity - Persian Empire Logo
History of Humanity - Greek History Logo
History of Humanity - Alexander the Great Logo
History of Humanity - Roman History Logo
History of Humanity - Punic Wars Logo
History of Humanity - Golden Age of Piracy Logo
History of Humanity - Revolutionary War Logo
History of Humanity - Mafia History Logo