# stri_match: Extract Regex Pattern Matches, Together with Capture Groups

## Description

These functions extract substrings in `str` that match a given regex `pattern`. Additionally, they extract matches to every *capture group*, i.e., to all the sub-patterns given in round parentheses.

## Usage

``` r
stri_match_all(str, ..., regex)

stri_match_first(str, ..., regex)

stri_match_last(str, ..., regex)

stri_match(str, ..., regex, mode = c("first", "all", "last"))

stri_match_all_regex(
  str,
  pattern,
  omit_no_match = FALSE,
  cg_missing = NA_character_,
  ...,
  opts_regex = NULL
)

stri_match_first_regex(
  str,
  pattern,
  cg_missing = NA_character_,
  ...,
  opts_regex = NULL
)

stri_match_last_regex(
  str,
  pattern,
  cg_missing = NA_character_,
  ...,
  opts_regex = NULL
)
```

## Arguments

|  |  |
|----|----|
| `str` | character vector; strings to search in |
| `...` | supplementary arguments passed to the underlying functions, including additional settings for `opts_regex` |
| `mode` | single string; one of: `'first'` (the default), `'all'`, `'last'` |
| `pattern`, `regex` | character vector; search patterns; for more details refer to [stringi-search](about_search.md) |
| `omit_no_match` | single logical value; if `FALSE`, then a row with missing values will indicate that there was no match; `stri_match_all_*` only |
| `cg_missing` | single string to be used if a capture group match is unavailable |
| `opts_regex` | a named list with <span class="pkg">ICU</span> Regex settings, see [`stri_opts_regex`](stri_opts_regex.md); `NULL` for default settings |

## Details

Vectorized over `str` and `pattern` (with recycling of the elements in the shorter vector if necessary). This allows to, for instance, search for one pattern in each given string, search for each pattern in one given string, and search for the i-th pattern within the i-th string.

If no pattern match is detected and `omit_no_match=FALSE`, then `NA`s are included in the resulting matrix (matrices), see Examples.

`stri_match`, `stri_match_all`, `stri_match_first`, and `stri_match_last` are convenience functions. They merely call `stri_match_*_regex` and are provided for consistency with other string searching functions\' wrappers, see, among others, [`stri_extract`](stri_extract.md).

## Value

For `stri_match_all*`, a list of character matrices is returned. Each list element represents the results of a different search scenario.

For `stri_match_first*` and `stri_match_last*` a character matrix is returned. Each row corresponds to a different search result.

The first matrix column gives the whole match. The second one corresponds to the first capture group, the third -- the second capture group, and so on.

If regular expressions feature a named capture group, the matrix columns will be named accordingly. However, for `stri_match_first*` and `stri_match_last*` this will only be the case if there is a single pattern.

## Author(s)

[Marek Gagolewski](https://www.gagolewski.com/) and other contributors

## See Also

The official online manual of <span class="pkg">stringi</span> at <https://stringi.gagolewski.com/>

Gagolewski M., <span class="pkg">stringi</span>: Fast and portable character string processing in R, *Journal of Statistical Software* 103(2), 2022, 1-59, [doi:10.18637/jss.v103.i02](https://doi.org/10.18637/jss.v103.i02)

Other search_extract: [`about_search`](about_search.md), [`stri_extract_all()`](stri_extract.md), [`stri_extract_all_boundaries()`](stri_extract_boundaries.md)

## Examples




``` r
stri_match_all_regex('breakfast=eggs, lunch=pizza, dessert=icecream',
   '(\\w+)=(\\w+)')
```

```
## [[1]]
##      [,1]               [,2]        [,3]      
## [1,] "breakfast=eggs"   "breakfast" "eggs"    
## [2,] "lunch=pizza"      "lunch"     "pizza"   
## [3,] "dessert=icecream" "dessert"   "icecream"
```

``` r
stri_match_all_regex(c('breakfast=eggs', 'lunch=pizza', 'no food here'),
   '(\\w+)=(\\w+)')
```

```
## [[1]]
##      [,1]             [,2]        [,3]  
## [1,] "breakfast=eggs" "breakfast" "eggs"
## 
## [[2]]
##      [,1]          [,2]    [,3]   
## [1,] "lunch=pizza" "lunch" "pizza"
## 
## [[3]]
##      [,1] [,2] [,3]
## [1,] NA   NA   NA
```

``` r
stri_match_all_regex(c('breakfast=eggs;lunch=pizza',
   'breakfast=bacon;lunch=spaghetti', 'no food here'),
   '(\\w+)=(\\w+)')
```

```
## [[1]]
##      [,1]             [,2]        [,3]   
## [1,] "breakfast=eggs" "breakfast" "eggs" 
## [2,] "lunch=pizza"    "lunch"     "pizza"
## 
## [[2]]
##      [,1]              [,2]        [,3]       
## [1,] "breakfast=bacon" "breakfast" "bacon"    
## [2,] "lunch=spaghetti" "lunch"     "spaghetti"
## 
## [[3]]
##      [,1] [,2] [,3]
## [1,] NA   NA   NA
```

``` r
stri_match_all_regex(c('breakfast=eggs;lunch=pizza',
   'breakfast=bacon;lunch=spaghetti', 'no food here'),
   '(?<when>\\w+)=(?<what>\\w+)')  # named capture groups
```

```
## [[1]]
##                       when        what   
## [1,] "breakfast=eggs" "breakfast" "eggs" 
## [2,] "lunch=pizza"    "lunch"     "pizza"
## 
## [[2]]
##                        when        what       
## [1,] "breakfast=bacon" "breakfast" "bacon"    
## [2,] "lunch=spaghetti" "lunch"     "spaghetti"
## 
## [[3]]
##         when what
## [1,] NA NA   NA
```

``` r
stri_match_first_regex(c('breakfast=eggs;lunch=pizza',
   'breakfast=bacon;lunch=spaghetti', 'no food here'),
   '(\\w+)=(\\w+)')
```

```
##      [,1]              [,2]        [,3]   
## [1,] "breakfast=eggs"  "breakfast" "eggs" 
## [2,] "breakfast=bacon" "breakfast" "bacon"
## [3,] NA                NA          NA
```

``` r
stri_match_last_regex(c('breakfast=eggs;lunch=pizza',
   'breakfast=bacon;lunch=spaghetti', 'no food here'),
   '(\\w+)=(\\w+)')
```

```
##      [,1]              [,2]    [,3]       
## [1,] "lunch=pizza"     "lunch" "pizza"    
## [2,] "lunch=spaghetti" "lunch" "spaghetti"
## [3,] NA                NA      NA
```

``` r
stri_match_first_regex(c('abcd', ':abcd', ':abcd:'), '^(:)?([^:]*)(:)?$')
```

```
##      [,1]     [,2] [,3]   [,4]
## [1,] "abcd"   NA   "abcd" NA  
## [2,] ":abcd"  ":"  "abcd" NA  
## [3,] ":abcd:" ":"  "abcd" ":"
```

``` r
stri_match_first_regex(c('abcd', ':abcd', ':abcd:'), '^(:)?([^:]*)(:)?$', cg_missing='')
```

```
##      [,1]     [,2] [,3]   [,4]
## [1,] "abcd"   ""   "abcd" ""  
## [2,] ":abcd"  ":"  "abcd" ""  
## [3,] ":abcd:" ":"  "abcd" ":"
```

``` r
# Match all the pattern of the form XYX, including overlapping matches:
stri_match_all_regex('ACAGAGACTTTAGATAGAGAAGA', '(?=(([ACGT])[ACGT]\\2))')[[1]][,2]
```

```
##  [1] "ACA" "AGA" "GAG" "AGA" "TTT" "AGA" "ATA" "AGA" "GAG" "AGA" "AGA"
```

``` r
# Compare the above to:
stri_extract_all_regex('ACAGAGACTTTAGATAGAGAAGA', '([ACGT])[ACGT]\\1')
```

```
## [[1]]
## [1] "ACA" "GAG" "TTT" "AGA" "AGA" "AGA"
```
