Overview
The word “grepl” stands for “grep logical”. The grepl() function in R simply searches for matches in characters or sequences of characters present in a given string.
Syntax
The syntax for the grepl method is as follows:
grepl(pattern, x, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE)Parameters
pattern: The character or sequence of characters that will be matched against the specified elements of the string.x: The specified string vector.ignore.case: IfTRUEi.e., it finds a match, the code ignores the upper or lowercase. This is optional.perl: This is a logical value. To know if perl-compatible regexps should be used or to know if the priority has been overextended. This is optional.fixed: This is a logical value. IfTRUE, then the pattern of the characters or sequence of characters is matched. This is optional.useBytes: This is a logical value. IfTRUE, the matching is simply done byte-by-byte instead of character-by-character. This makes the program faster and is optional.
Return value
The grepl() function returns FALSE or TRUE for matches in characters or a sequence of characters present in a string.
Example 1
# Creating string vector
x <- c("CAR", "BIKE")
See AlsoHow to Search Files Effectively in the Linux Terminalgrepl() in R | Hyperskill UniversityUse the Linux grep CommandAI Coding Assistant for Beginners# Calling grepL() function
grepl("CA", x)
From the output of the code:
[1] TRUE FALSEWe can see that it returns TRUE. This means that CA exists in the first item of the string variable CAR. FALSE means it is absent in the second item of the string variable BIKE.
Example 2
# creating a string variable
name <- c("CAR", "bIKE", "BICYCLE", "AEROPLANE")
# passing ignore.case argument to the grepl() function
grepl("bi", name, ignore.case = TRUE)
From the output of the code above:
[1] FALSE TRUE TRUE FALSEWe can see that it returns TRUE and TRUE for the second and third elements of the string variable, "bIKE" and "BICYCLE". This happens even though they are not all in the lower case like the argument we pass to the grepl() function. This way, the ignore.case parameter makes R ignore the cases of the texts.
Example 3
# creating a string variable
name <- c("CAR", "b|ke", "BICYCLE", "AEROPLANE")
grepl("b.", name, fixed = FALSE, perl=FALSE)
grepl("b.", name, fixed = TRUE, perl=FALSE)
From the output of the code with fixed = FALSE:
[1] FALSE TRUE FALSE FALSEIn a regular expression, the . metacharacter matches any single character. Therefore, the pattern b. will match any string in the name vector that has a b followed by any single character. As a result, it will return TRUE for element b|ke since it contains a b followed by another character.
From the output of the code with fixed = TRUE:
[1] FALSE FALSE FALSE FALSEWith fixed = TRUE, the . is interpreted literally, so it will only match the exact string b.. Since none of the elements in the name vector contain b., the function will return FALSE for all elements.
