The grep() function returns the indices of elements that match a pattern, while the grepl() function returns a logical vector indicating whether each element matches the pattern.
Key takeways:
grepl()checks for pattern matches in strings.
grepl()returns logical vector (TRUE/FALSE) indicating pattern presence.Parameters:
pattern: RegEx pattern to search
x: Character vector to search within
ignore.case:TRUEfor case-insensitive matching
perl:TRUEfor Perl-compatible regex
fixed:TRUEfor literal string matching
useBytes:TRUEfor byte-by-byte matchingThe use cases of
grepl()are filtering data, finding patterns, and text analysis.
Stephen Cole Kleene invented regular expressions (RegEx), which are powerful tools used for searching, matching, and manipulating text patterns. Using regular expressions can significantly enhance the efficiency and accuracy of these tasks. grepl() is a handy function in R for applying RegEx to efficiently identify matches in data. It is a useful tool in R, primarily used for pattern matching using regular expressions.
grepl() functionThe 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.
grepl() functionThe grep () helps with various tasks, such as quickly identifying and extracting rows that match a specific pattern, locating keywords or phrases in text data, and determining which elements of a character vector contain a given pattern.
grepl() in RThe syntax for the grepl method is as follows:
grepl(pattern, x, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE)
pattern: This is the character or sequence of characters that will be matched against the specified elements of the string.
x: This is the specified string vector.
ignore.case: If TRUE, i.e., it finds a match, the code ignores the upper or lowercase. This is optional.
perl: This determines whether Perl-compatible regular expressions (RegExps) should be used or if the priority has been exceeded. This is optional.
fixed: This is a logical value. If TRUE, then the pattern of the characters or sequence of characters is matched. This is optional.
useBytes: This is a logical value. If TRUE, the matching is simply done byte-by-byte instead of character-by-character. This makes the program faster; this is also optional.
The grepl() function returns FALSE or TRUE depending on whether a match is found in a character or sequence of characters within a string.
grepl() for basic pattern matchingLet’s see the code below:
# Creating string vectorx <- c("CAR", "BIKE")# Calling grepL() functiongrepl("CA", x)
From the output of the code:
[1] TRUE FALSE
We 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.
ignore.case of grepl()Let’s see the code below:
# creating a string vectorname <- c("CAR", "bIKE", "BICYCLE", "AEROPLANE")# passing ignore.case argument to the grepl() functiongrepl("bi", name, ignore.case = TRUE)
From the output of the code above:
[1] FALSE TRUE TRUE FALSE
We can see that it returns TRUE for the second and third elements of the string variable, "bIKE" and "BICYCLE". This happens even though they are not all in lowercase, like the argument we pass to the grepl() function. This way, the ignore.case parameter makes a case-insensitive search with grepl() in R.
perl and fixed parameters in the grepl()Let's see the code below:
# creating a string vectorname <- c("CAR", "b|ke", "BICYCLE", "AEROPLANE")# Without fixed parametergrepl("b.", name, fixed = FALSE)# With fixed parametergrepl("b.", name, fixed = TRUE)# creating another vectorphrases <- c("Good Educative platform", "Educative good platform", "Educative platform", "R course Educative platform", "platform Educative")# using grepl() with a Perl-compatible RegEx patternresult_perl <- grepl("(?<=\\bEducative\\s)platform\\b", phrases, perl = TRUE)# displaying the resultprint(result_perl)
From the output of the code with fixed = FALSE:
[1] FALSE TRUE FALSE FALSE
In 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 FALSE
With 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.
From the output of the code with perl = TRUE:
[1] TRUE FALSE TRUE TRUE FALSE
With perl = TRUE, the Perl-compatible RegEx pattern (?<=\\bEducative\\s)platform\\b matches the word “platform” only if it is preceded by the word “Educative” and a space. Here, (?<=) is a look behind the assertion ensuring “Educative” appears before “platform.” The \\b denotes word boundaries, confirming that both “Educative” and “platform” are treated as complete words. The \\s matches a space character, ensuring “Educative” is followed by a space.
Quiz!
What does grepl() stand for in R?
Graphical regular expression locator
General regular expression pattern locator
Grep logical
None of the above
In summary, the grepl() function is used for R pattern matching in text data, leveraging regular expressions to efficiently find matches and extract information. Understanding its parameters and return values can help us complete data manipulation and R data analysis tasks.
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