stringr::str_detect()
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Description

The str_detect() function is part of the {stringr} package, which is part of the {tidyverse}.

We use the str_detect() function to ask if it is TRUE or FALSE that a certain pattern is present in a string or array of strings. A common usage of this function is with dplyr::filter() to subset rows from tibbles (data frames) that contain (or do not contain) a certain substring or regular expression (a special kind of pattern-matching string).

All {stringr} functions (and R itself) are case sensitive, which means uppercase and lowercase letters are viewed as different characters. In other words, searching for “A” will not match “a”, and searching for “a” will not match “A.”

To use this function, you need to either first load the {stringr} library, or always use the function with stringr::str_detect() notation.

# Load the library
library(stringr)
# Or, load the full tidyverse:
library(tidyverse)

# Or, use :: notation
stringr::str_detect()

Conceptual Usage

stringr::str_detect("string to search in", "substring to look for in bigger string")

stringr::str_detect(c("array", "of", "strings", "to", "search", "in"), 
                   "substring to look for in each string in the array")

Examples

The examples use the variables shown below, as well as the carnivores dataset. Learn more about the carnivores with get_help("carnivores").

# Show all variables and datasets used in examples:

# A single string
single_sentence
## [1] "No doubt about the way the wind blows."

# An array of strings
fruits
## [1] "kiwi fruit" "pomelo"     "goji berry" "persimmon"  "mulberry"   "raspberry"

# A tibble
carnivores
## # A tibble: 9 × 4
##   name              genus        awake brainwt
##   <chr>             <fct>        <dbl>   <dbl>
## 1 Arctic fox        Vulpes        11.5  0.0445
## 2 Cheetah           Acinonyx      11.9 NA     
## 3 Dog               Canis         13.9  0.07  
## 4 Gray seal         Haliochoerus  17.8  0.325 
## 5 Jaguar            Panthera      13.6  0.157 
## 6 Lion              Panthera      10.5 NA     
## 7 Northern fur seal Callorhinus   15.3 NA     
## 8 Red fox           Vulpes        14.2  0.0504
## 9 Tiger             Panthera       8.2 NA


# Does the word "way" appear in single sentence?
str_detect(single_sentence, "way")
## [1] TRUE


# Does the capitalized word "Wind" appear in single sentence?
str_detect(single_sentence, "Wind")
## [1] FALSE


# Does the word "berry" appear in each string in fruits?
str_detect(fruits, "berry")
## [1] FALSE FALSE  TRUE FALSE  TRUE  TRUE


# Keep only rows where it is `TRUE` that the word "seal" is in `name`, using dplyr::filter
carnivores %>%
  dplyr::filter(str_detect(name, "seal"))
## # A tibble: 2 × 4
##   name              genus        awake brainwt
##   <chr>             <fct>        <dbl>   <dbl>
## 1 Gray seal         Haliochoerus  17.8   0.325
## 2 Northern fur seal Callorhinus   15.3  NA


# Keep only rows where it is `FALSE` that the word "fox" is in `name`, using dplyr::filter
# For this, we negate the result of `str_detect()` using `!` to get `FALSE` instead of `TRUE`
carnivores %>%
  dplyr::filter(!str_detect(name, "fox"))
## # A tibble: 7 × 4
##   name              genus        awake brainwt
##   <chr>             <fct>        <dbl>   <dbl>
## 1 Cheetah           Acinonyx      11.9  NA    
## 2 Dog               Canis         13.9   0.07 
## 3 Gray seal         Haliochoerus  17.8   0.325
## 4 Jaguar            Panthera      13.6   0.157
## 5 Lion              Panthera      10.5  NA    
## 6 Northern fur seal Callorhinus   15.3  NA    
## 7 Tiger             Panthera       8.2  NA