```r
chapters_gamma <- chapters_gamma %>%
  separate(document, c("title", "chapter"), sep = "_", convert = TRUE)

chapters_gamma
```

```
## # A tibble: 772 x 4
##    title                 chapter topic     gamma
##    <chr>                   <int> <int>     <dbl>
##  1 Great Expectations         57     1 0.0000135
##  2 Great Expectations          7     1 0.0000147
##  3 Great Expectations         17     1 0.0000212
##  4 Great Expectations         27     1 0.0000192
##  5 Great Expectations         38     1 0.354    
##  6 Great Expectations          2     1 0.0000172
##  7 Great Expectations         23     1 0.551    
##  8 Great Expectations         15     1 0.0168   
##  9 Great Expectations         18     1 0.0000127
## 10 The War of the Worlds      16     1 0.0000108
## # … with 762 more rows
```