Extracting specific data from nested list - r

Question

I am trying web scraping of movies of 2019 from IMDB. I am extracting the Director's name from a nested list.
Now, the issue is the name of the Directors are not given for all the movies but for selected few, hence I need to extract the Director's name where ever the term 'Director:\n' appears.
The nested list is as follows:
[[1]]
[1] "Henry Cavill,Freya Allan,Anya Chalotra,Mimi Ndiweni\n"
[[2]]
[1] "\n"
[2] "Director:\nJ.J. Abrams"
[3] "|"
[4] "Stars:\nCarrie Fisher,Mark Hamill,Adam Driver,Daisy Ridley\n"
[[3]]
[1] "Pedro Pascal,Carl Weathers,Rio Hackford,Gina Carano\n"
[[4]]
[1] "\n"
[2] "Director:\nTom Hooper"
[3] "|"
[4] "Stars:\nFrancesca Hayward,Taylor Swift,Laurie Davidson,Robbie Fairchild\n"
[[5]]
[1] "Guy Pearce,Andy Serkis,Stephen Graham,Joe Alwyn\n"
[[6]]
[1] "\n"
[2] "Director:\nMichael Bay"
[3] "|"
[4] "Stars:\nRyan Reynolds,Mélanie Laurent,Manuel Garcia-Rulfo,Ben Hardy\n"
Here as one can see, the Director's name appears in an alternate manner but this is just for example purpose. Thanks in advance.
Expected Output:
directors_data
NA,"J.J. Abrams",NA,"Michael Bay"

Answer 1

Here is a base R solution, where you can use use the method grep+gsub, or the method regmatches + gregexpr.
Assuming you data is a list lst, then you can try the following code to extract the director's name:
sapply(lst, function(x) ifelse(length(r <- grep("Director",x,value = T)),gsub("Director:\n","",r),NA))
or
sapply(lst, function(x) ifelse(length(r<-unlist(regmatches(x,gregexpr("(?<=Director:\n)(.*)",x,perl = T)))),r,NA))

Answer 2

You can use str_extract to extract string and map to loop over each element in the list
library(purrr)
library(stringr)
map_chr(list_df, ~{temp <- na.omit(str_extract(.x, "(?<=Director:\n)(.*)"));
if(length(temp) > 0) temp else NA})
#[1] NA "J.J. Abrams" NA "Tom Hooper"
data
Since you did not provide a reproducible example I created one myself.
list_df <- list("Henry Cavill,Freya Allan,Anya Chalotra,Mimi Ndiweni\n",
c("\n", "Director:\nJ.J. Abrams", "|", "Stars:\nCarrie Fisher,Mark Hamill,Adam Driver,Daisy Ridley\n"
), "Pedro Pascal,Carl Weathers,Rio Hackford,Gina Carano\n",
c("\n", "Director:\nTom Hooper", "|", "Stars:\nFrancesca Hayward,Taylor Swift,Laurie Davidson,Robbie Fairchild\n"
))

Answer 3

Base R solution:
directors_data <- gsub("Director:\n", "",
unlist(Map(function(x){x[2]}, list_df)), fixed = TRUE)
Base R solution not using unlist and using mapply not Map:
directors_data <- gsub(".*\\\n", "",
mapply(function(x){x[2]}, list_df, SIMPLIFY = TRUE))
Base R solution if pattern appears at different indices per list element:
directors_data <- gsub(".*\\\n", "",
mapply(function(x) {
ifelse(length(x[which(grepl("Director", x))]) > 0,
x[which(grepl("Director", x))],
NA)}, list_df, SIMPLIFY = TRUE))