Vectorised over `string`

and `pattern`

.

str_extract(string, pattern)
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 stringi-search-regex. Control options with
`regex()` .
Match a fixed string (i.e. by comparing only bytes), using
`fixed(x)` . This is fast, but approximate. Generally,
for matching human text, you'll want `coll(x)` 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")` . |

simplify |
If `FALSE` , the default, returns a list of character
vectors. If `TRUE` returns a character matrix. |

## Value

A character vector.

## See also

`str_match`

to extract matched groups;
`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"

# 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"

#> [[1]]
#> [1] "This" "is" "suprisingly" "a" "sentence"
#>