stringr::str_extract all elements of a list R

Question

I'm trying to get all the "banana + word" ocurrences of a given object, but the str_extract returns only the first occurence. My code:

all_terms <- c("banana word2 word3 word4 banana split word2 word3 word4",
               "x y z",
               "banana ice cream")

banana_terms <- all_terms %>% 
  str_extract("banana.+") %>% 
  word(1,2)


banana_terms
Out: [1] "banana word2" NA             "banana ice"

What I wanted:

Out: [1] "banana word2" "banana split", "banana ice"

score 4 · Accepted Answer · answered Apr 19 '22 at 15:24

4

Use str_extract_all and \\w+ to get the word after banana (and banana).

all_terms %>% 
  str_extract_all("banana.\\w+") %>% 
  unlist()

# [1] "banana word2" "banana split" "banana ice"

Without unlist, you get a list:

str_extract_all(all_terms, "banana.\\w+")

[[1]]
[1] "banana word2" "banana split"

[[2]]
character(0)

[[3]]
[1] "banana ice"

answered Apr 19 '22 at 15:24

Maël

45,206
3
29
67

It works! Can you explain me what is the \\w ? Is it word? I could not find in my cheat sheet (https://spannbaueradam.shinyapps.io/r_regex_tester/) – jvqp Apr 19 '22 at 15:38
Basically yes, look [here](https://stackoverflow.com/questions/11874234/difference-between-w-and-b-regular-expression-meta-characters) maybe for more info. – Maël Apr 19 '22 at 15:41

score 2 · Answer 2 · answered Apr 19 '22 at 15:47

2

In base R, we can use regmatches/gregexpr

unlist(regmatches(all_terms, gregexpr("banana\\s+\\S+", all_terms)))
[1] "banana word2" "banana split" "banana ice"

answered Apr 19 '22 at 15:47

akrun

874,273
37
540
662

score 1 · Answer 3 · answered Apr 19 '22 at 15:40

If you want to use str_extract, you need to make sure each "banana word" is an individual element in a vector.

str_split is used to split every "empty space" + "banana" pattern (" (?=banana)") into individual element. Then use the regex (banana.\\w+) provided by @Maël in str_extract.

Finally, remove NA in the vector.

library(stringr)

all_banana <- str_extract(str_split(all_terms, " (?=banana)", simplify = T), "banana.\\w+")
all_banana <- all_banana[!is.na(all_banana)]

all_banana
[1] "banana word2" "banana ice"   "banana split"

stringr::str_extract all elements of a list R

3 Answers3