Inverse matching with stringr

Question

I want to remove all characters which doesn't match a string pattern using stringr package. So far I've been able to remove those before the pattern using "\\w+(?= (grape|satsuma))" as pattern but remove those after the pattern is still imposible.

> str_remove_all("apples grape banana melon olive persimon grape apples satsuma papaya", 
+                "\\w+(?= (grape|satsuma))")
[1] " grape banana melon olive  grape  satsuma papaya"

The desired result is:

"grape grape satsuma"

(NOTE: I am aware the easiest approach in this case is to extract only "grape" and "satsuma" but for analysis purposes I prefer this way)

Edited providing the entire problem

The entire problem is as follow, given a d data frame which contains a column with a string the function should return the same column only with matches:

> d
# A tibble: 2 x 2
  string_column                  c2
  <chr>                       <dbl>
1 apples grape banana satsuma     3
2 grape banana satsuma melon      4

Using the answer provided by @d.r works:

> d %>% 
+   mutate_at(vars(string_column), ~ gsub("(grape|satsuma| )(*SKIP)(*FAIL)|.", "", ., perl = TRUE))

# A tibble: 2 x 2
  string_column        c2
  <chr>             <dbl>
1 " grape  satsuma"     3
2 "grape  satsuma "     4

All answers provided so far using stringr package fail returning the string_column

This the dput for d:

d <- structure(list(string_column = c("apples grape banana satsuma", 
"grape banana satsuma melon"), c2 = c(3, 4)), row.names = c(NA, 
-2L), class = c("tbl_df", "tbl", "data.frame"))

Answer 1

You may want to look at negative lookaheads and some related regex techniques in the linked thread.

However, since we are extracting words I'd rather use str_extract_all and I'd do it like this:

str_extract_all("apples grape banana melon olive persimon grape apples satsuma papaya", 
                               "grape|satsuma")

 "grape"   "grape"   "satsuma"

I also really like this line that @steveLangsford left in a comment:

paste0(unlist(str_extract_all("apples grape banana melon olive persimon grape apples satsuma papaya", "grape|satsuma")), collapse=" ") 

"grape grape satsuma"

Taking it a little bit further based on our discussion/comments:

string_column <- c("apples grape banana satsuma", "grape banana satsuma melon") 
c2            <- c(3, 4) 
d             <- tibble(string_column,c2) 

myfun <- function(x) {paste0(unlist(str_extract_all(x, "grape|satsuma")), collapse=" ") }

sapply(d$string_column, myfun)

        "grape satsuma"             "grape satsuma"