Left joining a table to itself
So far, you've been inner joining a table to itself in order to find the children of themes like "Harry Potter" or "The Lord of the Rings".
But some themes might not have any children at all, which means they won't be included in the inner join. As you've learned in this chapter, you can identify those with a left_join and a filter().
Questo esercizio fa parte del corso
Joining Data with dplyr
Istruzioni dell'esercizio
- Left join the themes table to its own children, with the suffixes
_parentand_childrespectively. - Filter the result of the join to find themes that have no children.
Esercizio pratico interattivo
Prova a risolvere questo esercizio completando il codice di esempio.
themes %>%
# Left join the themes table to its own children
___ %>%
# Filter for themes that have no child themes
filter(___)