grep()

grep(pattern, x, value = FALSE, ignore.case = FALSE, perl = FALSE, fixed = FALSE, useBytes = FALSE, invert = FALSE)

grep() searches for matches to a pattern in a character vector and returns the indices of elements that match.

Syntax

grep(pattern, x, value = FALSE, ignore.case = FALSE, 
     perl = FALSE, fixed = FALSE, useBytes = FALSE, invert = FALSE)

Parameters

Parameter	Type	Default	Description
pattern	character	—	A regular expression pattern to match
x	character	—	A character vector to search in
value	logical	FALSE	If TRUE, return the matching strings instead of indices
ignore.case	logical	FALSE	If TRUE, ignore case when matching
perl	logical	FALSE	If TRUE, use Perl-compatible regular expressions
fixed	logical	FALSE	If TRUE, treat pattern as a literal string (faster)
useBytes	logical	FALSE	If TRUE, match byte-by-byte rather than character-by-character
invert	logical	FALSE	If TRUE, return indices of elements that do NOT match

Examples

Basic usage

fruits <- c("apple", "banana", "cherry", "date", "elderberry")

grep("a", fruits)
# [1] 1 2 4

Using value = TRUE

grep("a", fruits, value = TRUE)
# [1] "apple"    "banana"   "date"

Case-insensitive matching

colors <- c("Red", "GREEN", "blue", "YELLOW")

grep("red", colors, ignore.case = TRUE, value = TRUE)
# [1] "Red"   "GREEN"

Fixed string matching (faster)

emails <- c("user@example.com", "test@domain.org", "invalid")

grep("@", emails, fixed = TRUE, value = TRUE)
# [1] "user@example.com" "test@domain.org"

Invert to find non-matches

grep("a", fruits, invert = TRUE, value = TRUE)
# [1] "cherry"    "elderberry"

Common Patterns

Counting matches

length(grep("pattern", strings))

Filtering data frames

df[grep("pattern", df$column), ]

Multiple patterns (OR logic)

grep("apple|orange", fruits, value = TRUE)

See Also

• stringr::grepl
• stringr::gsub
• stringr::sub