Grabbing the context of regular expression matches

context.R

library(stringr)
library(dplyr)
library(purrr)
library(rlang)
library(text2vec) # for movie reviews data

# favor stringr over base R because stringr handles NAs whereas base R returns
# zero length, base R below:
# regmatches(string, regexpr(x, string, ignore.case = ignore_case))
pattern_context <- function(string, pattern, n_before = 10, n_after = 10, 
                            ignore_case = TRUE, first = TRUE) {
  x <- paste0(".{0,", n_before, "}", pattern, ".{0,", n_after, "}")
  
  if (first)
    stringr::str_extract(string, stringr::regex(pattern = x, ignore_case = ignore_case))
  else
    stringr::str_extract_all(string, stringr::regex(pattern = x, ignore_case = ignore_case))
}

pattern_context_df <- function(.data, ..., cols = everything()) {
  df_context <- .data %>% 
    dplyr::select({{ cols }}) %>% 
    purrr::map(pattern_context, ...) %>% 
    dplyr::bind_cols()
  
  names(df_context) <- paste0(names(df_context), "_context")
  
  df <- dplyr::bind_cols(.data, df_context)
  df[, order(colnames(df))]
}

# create variables
movie_review %>% 
  as_tibble() %>% 
  mutate(
    bad_context = pattern_context(review, "bad"), 
    good_context = pattern_context(review, "good"), 
  ) %>% 
  select(review:good_context)
#> # A tibble: 5,000 x 3
#>    review                              bad_context       good_context      
#>    <chr>                               <chr>             <chr>             
#>  1 With all this stuff going down at ~ drugs are bad m'~ <NA>              
#>  2 "\\\"The Classic War of the Worlds~ <NA>              <NA>              
#>  3 The film starts with a manager (Ni~ oments is badly ~ ivers the goods w~
#>  4 "It must be assumed that those who~ <NA>              ng of the Good Fr~
#>  5 "Superbly trashy and wondrously un~ <NA>              <NA>              
#>  6 I dont know why people think this ~ is such a bad mo~ " a pretty good p~
#>  7 This movie could have been very go~ "me really bad m~ been very good, b~
#>  8 I watched this video at a friend's~ cience is bad, a~ <NA>              
#>  9 A friend of mine bought this film ~ <NA>              <NA>              
#> 10 "<br /><br />This movie is full of~ <NA>              <NA>              
#> # ... with 4,990 more rows

# create variable for every column
movie_review %>% 
  as_tibble() %>% 
  select(id, review) %>% 
  pattern_context_df("good")
#> # A tibble: 5,000 x 4
#>    id     id_context review                             review_context     
#>    <chr>  <chr>      <chr>                              <chr>              
#>  1 5814_8 <NA>       With all this stuff going down at~ <NA>               
#>  2 2381_9 <NA>       "\\\"The Classic War of the World~ <NA>               
#>  3 7759_3 <NA>       The film starts with a manager (N~ ivers the goods wi~
#>  4 3630_4 <NA>       "It must be assumed that those wh~ ng of the Good Fri~
#>  5 9495_8 <NA>       "Superbly trashy and wondrously u~ <NA>               
#>  6 8196_8 <NA>       I dont know why people think this~ " a pretty good pl~
#>  7 7166_2 <NA>       This movie could have been very g~ been very good, bu~
#>  8 10633~ <NA>       I watched this video at a friend'~ <NA>               
#>  9 319_1  <NA>       A friend of mine bought this film~ <NA>               
#> 10 8713_~ <NA>       "<br /><br />This movie is full o~ <NA>               
#> # ... with 4,990 more rows

# create variable for specified columns
movie_review %>% 
  as_tibble() %>% 
  select(id, review) %>% 
  pattern_context_df("good", cols = review)
#> # A tibble: 5,000 x 3
#>    id      review                                      review_context      
#>    <chr>   <chr>                                       <chr>               
#>  1 5814_8  With all this stuff going down at the mome~ <NA>                
#>  2 2381_9  "\\\"The Classic War of the Worlds\\\" by ~ <NA>                
#>  3 7759_3  The film starts with a manager (Nicholas B~ ivers the goods wit~
#>  4 3630_4  "It must be assumed that those who praised~ ng of the Good Frid~
#>  5 9495_8  "Superbly trashy and wondrously unpretenti~ <NA>                
#>  6 8196_8  I dont know why people think this is such ~ " a pretty good plo~
#>  7 7166_2  This movie could have been very good, but ~ been very good, but~
#>  8 10633_1 I watched this video at a friend's house. ~ <NA>                
#>  9 319_1   A friend of mine bought this film for 1, a~ <NA>                
#> 10 8713_10 "<br /><br />This movie is full of referen~ <NA>                
#> # ... with 4,990 more rows

# create variable for all columns except specified
movie_review %>% 
  as_tibble() %>% 
  select(id, review) %>% 
  pattern_context_df("good", cols = -id)
#> # A tibble: 5,000 x 3
#>    id      review                                      review_context      
#>    <chr>   <chr>                                       <chr>               
#>  1 5814_8  With all this stuff going down at the mome~ <NA>                
#>  2 2381_9  "\\\"The Classic War of the Worlds\\\" by ~ <NA>                
#>  3 7759_3  The film starts with a manager (Nicholas B~ ivers the goods wit~
#>  4 3630_4  "It must be assumed that those who praised~ ng of the Good Frid~
#>  5 9495_8  "Superbly trashy and wondrously unpretenti~ <NA>                
#>  6 8196_8  I dont know why people think this is such ~ " a pretty good plo~
#>  7 7166_2  This movie could have been very good, but ~ been very good, but~
#>  8 10633_1 I watched this video at a friend's house. ~ <NA>                
#>  9 319_1   A friend of mine bought this film for 1, a~ <NA>                
#> 10 8713_10 "<br /><br />This movie is full of referen~ <NA>                
#> # ... with 4,990 more rows