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().

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Joining Data with dplyr

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Instructions

Left join the themes table to its own children, with the suffixes _parent and _child respectively.
Filter the result of the join to find themes that have no children.

Exercice interactif pratique

Essayez cet exercice en complétant cet exemple de code.

themes %>% 
  # Left join the themes table to its own children
  ___ %>%
  # Filter for themes that have no child themes
  filter(___)

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