problem extracting matching sentence from column in data frame

General
5

You can do something like this.

library(dplyr)

iris %>%
  count(Species) %>% # Example data
  mutate(Prep = ifelse(grepl("virginica", Species), "virginica", NA))
#> # A tibble: 3 x 3
#>   Species        n Prep     
#>   <fct>      <int> <chr>    
#> 1 setosa        50 <NA>     
#> 2 versicolor    50 <NA>     
#> 3 virginica     50 virginica

It would be easier to help you, if you could provide a minimal REPRoducible EXample (reprex)