Extract the complete match

str_extract() extracts the first complete match from each string, str_extract_all()extracts all matches from each string.

Usage

str_extract(string, pattern, group = NULL)

str_extract_all(string, pattern, simplify = FALSE)

Arguments

string

Input vector. Either a character vector, or something coercible to one.

pattern

Pattern to look for.

The default interpretation is a regular expression, as described in vignette("regular-expressions"). Use regex() for finer control of the matching behaviour.

Match a fixed string (i.e. by comparing only bytes), using fixed(). This is fast, but approximate. Generally, for matching human text, you'll want coll() which respects character matching rules for the specified locale.

Match character, word, line and sentence boundaries with boundary(). An empty pattern, "", is equivalent to boundary("character").

group

If supplied, instead of returning the complete match, will return the matched text from the specified capturing group.

simplify

A boolean.

• FALSE (the default): returns a list of character vectors.

• TRUE: returns a character matrix.

Value

• str_extract(): an character vector the same length as string/pattern.

• str_extract_all(): a list of character vectors the same length as string/pattern.

See also

str_match() to extract matched groups; stringi::stri_extract() for the underlying implementation.

Examples

shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2")
str_extract(shopping_list, "\\d")
#> [1] "4" NA  NA  "2"
str_extract(shopping_list, "[a-z]+")
#> [1] "apples" "bag"    "bag"    "milk"  
str_extract(shopping_list, "[a-z]{1,4}")
#> [1] "appl" "bag"  "bag"  "milk"
str_extract(shopping_list, "\\b[a-z]{1,4}\\b")
#> [1] NA     "bag"  "bag"  "milk"

str_extract(shopping_list, "([a-z]+) of ([a-z]+)")
#> [1] NA             "bag of flour" "bag of sugar" NA            
str_extract(shopping_list, "([a-z]+) of ([a-z]+)", group = 1)
#> [1] NA    "bag" "bag" NA   
str_extract(shopping_list, "([a-z]+) of ([a-z]+)", group = 2)
#> [1] NA      "flour" "sugar" NA     

# Extract all matches
str_extract_all(shopping_list, "[a-z]+")
#> [[1]]
#> [1] "apples" "x"     
#> 
#> [[2]]
#> [1] "bag"   "of"    "flour"
#> 
#> [[3]]
#> [1] "bag"   "of"    "sugar"
#> 
#> [[4]]
#> [1] "milk" "x"   
#> 
str_extract_all(shopping_list, "\\b[a-z]+\\b")
#> [[1]]
#> [1] "apples"
#> 
#> [[2]]
#> [1] "bag"   "of"    "flour"
#> 
#> [[3]]
#> [1] "bag"   "of"    "sugar"
#> 
#> [[4]]
#> [1] "milk"
#> 
str_extract_all(shopping_list, "\\d")
#> [[1]]
#> [1] "4"
#> 
#> [[2]]
#> character(0)
#> 
#> [[3]]
#> character(0)
#> 
#> [[4]]
#> [1] "2"
#> 

# Simplify results into character matrix
str_extract_all(shopping_list, "\\b[a-z]+\\b", simplify = TRUE)
#>      [,1]     [,2] [,3]   
#> [1,] "apples" ""   ""     
#> [2,] "bag"    "of" "flour"
#> [3,] "bag"    "of" "sugar"
#> [4,] "milk"   ""   ""     
str_extract_all(shopping_list, "\\d", simplify = TRUE)
#>      [,1]
#> [1,] "4" 
#> [2,] ""  
#> [3,] ""  
#> [4,] "2" 

# Extract all words
str_extract_all("This is, suprisingly, a sentence.", boundary("word"))
#> [[1]]
#> [1] "This"        "is"          "suprisingly" "a"           "sentence"   
#>