stringr::str_detect()

str_detect(string, pattern, regex = TRUE)

The str_detect() function from stringr detects whether a pattern exists within a string. It returns a logical vector indicating which strings contain the match, making it useful for filtering, conditional operations, and subsetting string data.

Syntax

str_detect(string, pattern, regex = TRUE)

Parameters

Parameter	Type	Default	Description
string	character	Required	A character vector to search
pattern	pattern	Required	A pattern to look for (regex, fixed, or coll)
regex	logical	TRUE	If TRUE, pattern is interpreted as a regular expression

Examples

Basic usage

library(stringr)

# Detect a simple substring
strings <- c("apple", "banana", "cherry", "date")
str_detect(strings, "a")
# [1]  TRUE  TRUE FALSE  TRUE

Using with dplyr filter

library(dplyr)

fruits <- data.frame(
  name = c("apple", "banana", "cherry", "date", "apricot"),
  color = c("red", "yellow", "red", "brown", "orange")
)

# Filter rows where name contains "a"
fruits %>% filter(str_detect(name, "a"))
#    name   color
# 1  apple     red
# 2 banana  yellow
# 3  apricot orange

Regex patterns

# Detect strings starting with "a"
str_detect(c("apple", "banana", "apricot"), "^a")
# [1]  TRUE FALSE  TRUE

# Detect strings ending with "e"
str_detect(c("apple", "banana", "cherry"), "e$")
# [1]  TRUE FALSE  TRUE

# Detect strings containing any digit
str_detect(c("abc123", "def", "xyz789"), "\\\\d")
# [1]  TRUE FALSE  TRUE

Case-insensitive matching

# Default is case-sensitive
str_detect("Apple", "apple")
# [1] FALSE

# Use regex with (?i) for case-insensitive
str_detect("Apple", "(?i)apple")
# [1] TRUE

# Or use fixed() for exact matching
str_detect("Apple", fixed("apple", ignore_case = TRUE))
# [1] TRUE

Detecting multiple patterns

# Detect any of multiple patterns using |
str_detect(c("cat", "dog", "bat"), "cat|dog")
# [1]  TRUE  TRUE FALSE

Common Patterns

• With dplyr::mutate: Add a column indicating pattern match
• With dplyr::filter: Subset rows based on string content
• With sum(): Count matching strings
• With which(): Get indices of matching strings

Combined with mutate

library(dplyr)

df <- data.frame(
  email = c("user1@example.com", "invalid", "user2@test.org", "another.invalid")
)

df \%>\%
  mutate(
    is_valid_email = str_detect(email, "@.*\\\\.")
  )
#                  email is_valid_email
# 1   user1@example.com          TRUE
# 2               invalid         FALSE
# 3    user2@test.org          TRUE
# 4      another.invalid         FALSE

Counting matches

strings <- c("apple", "banana", "cherry", "date", "apricot")

# Count how many strings contain "a"
sum(str_detect(strings, "a"))
# [1] 4

See Also

• dplyr::filter
• purrr::map