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Add warning message to joins chapter

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Hadley Wickham 2022-09-18 16:23:42 -05:00
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joins.qmd
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@ -25,6 +25,11 @@ If you're familiar with SQL, you should find the ideas in this chapter familiar,
### Prerequisites
::: callout-important
This chapter relies on features only found in the development version of dplyr.
If you want to live life on the edge you can get the dev version with `devtools::install_github("tidyverse/dplyr")`.
:::
We'll explore the five related datasets from nycflights13 using the join functions from dplyr.
```{r}
@ -329,7 +334,8 @@ airports |>
```
**Anti-joins** are the opposite: they return all rows in `x` that don't have a match in `y`.
They're useful for finding missing values that are **implicit** in the data, the topic of @sec-missing-implicit. Implicitly missing values don't show up as explicit `NA`s but instead only exist as an absence.
They're useful for finding missing values that are **implicit** in the data, the topic of @sec-missing-implicit.
Implicitly missing values don't show up as explicit `NA`s but instead only exist as an absence.
For example, we can find rows that should be in `airports` by looking for flights that don't have a matching destination:
```{r}