Opposite of unnest_tokens

library(tidyverse)
tidy_austen %>% 
     group_by(book,linenumber) %>% 
     summarise(text = str_c(word, collapse = " "))

Not a stupid question! The answer depends a bit on exactly what you are trying to do, but here would be my typical approach if I wanted to get my text back to its original form after some processing in its tidied form, using the group_by() function from dplyr.

First, let's go from raw text to a tidied format.

library(tidyverse)
library(tidytext)

tidy_austen <- janeaustenr::austen_books() %>%
    group_by(book) %>%
    mutate(linenumber = row_number()) %>%
    ungroup() %>%
    unnest_tokens(word, text)

tidy_austen
#> # A tibble: 725,055 x 3
#>    book                linenumber word       
#>    <fct>                    <int> <chr>      
#>  1 Sense & Sensibility          1 sense      
#>  2 Sense & Sensibility          1 and        
#>  3 Sense & Sensibility          1 sensibility
#>  4 Sense & Sensibility          3 by         
#>  5 Sense & Sensibility          3 jane       
#>  6 Sense & Sensibility          3 austen     
#>  7 Sense & Sensibility          5 1811       
#>  8 Sense & Sensibility         10 chapter    
#>  9 Sense & Sensibility         10 1          
#> 10 Sense & Sensibility         13 the        
#> # … with 725,045 more rows

The text is tidy now! But we can untidy it, back to something sort of like its original form. I typically approach this using group_by() and summarize() from dplyr, and str_c() from stringr. What does the text look like at the end, in this particular case?

tidy_austen %>% 
    group_by(book, linenumber) %>% 
    summarize(text = str_c(word, collapse = " ")) %>%
    ungroup()
#> # A tibble: 62,272 x 3
#>    book            linenumber text                                         
#>    <fct>                <int> <chr>                                        
#>  1 Sense & Sensib…          1 sense and sensibility                        
#>  2 Sense & Sensib…          3 by jane austen                               
#>  3 Sense & Sensib…          5 1811                                         
#>  4 Sense & Sensib…         10 chapter 1                                    
#>  5 Sense & Sensib…         13 the family of dashwood had long been settled…
#>  6 Sense & Sensib…         14 was large and their residence was at norland…
#>  7 Sense & Sensib…         15 their property where for many generations th…
#>  8 Sense & Sensib…         16 respectable a manner as to engage the genera…
#>  9 Sense & Sensib…         17 surrounding acquaintance the late owner of t…
#> 10 Sense & Sensib…         18 man who lived to a very advanced age and who…
#> # … with 62,262 more rows

^{Created on 2019-07-11 by the reprex package (v0.3.0)}