Data Wrangling 2

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# Data Wrangling 2
### Bora Jin

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## Material

🎥 Watch [Working With Multiple Data Frames](https://youtu.be/VdV5ABsaf5Y)

- [Slides](https://rstudio-education.github.io/datascience-box/course-materials/slides/u2-d08-multi-df/u2-d08-multi-df.html#1)

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## Today's Goal

- Combine data from different sources using a well-chosen join function in the format `something_join(x, y)`:

- `left_join()`: return all rows from `x` for all columns in `x` and `y`
  - `right_join()`: return all rows from `y` for all columns in `x` and `y`
  - `full_join()`: return all rows from both `x` and `y` for all columns in `x` and `y`
  - `inner_join()`: return all rows from `x` where there are matching values in `y`, returning
all combination of multiple matches in the case of multiple matches for all columns in `x` and `y`
  - `semi_join()`: return all rows from `x` where there are matching values in `y`, keeping just columns from `x`   
  - `anti_join()`: return all rows from `x` where there are not matching values in `y`, keeping just columns from `x`   
  - `\(\cdots\)`

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## Quiz

**Q - Which join function might you use when you want to expand `x` by appending all variables in `y` for all the rows in `x`?**

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## Quiz

**Q - Which join function might you use when you want a dataset with all the rows and the columns in `x` and `y`?**

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## Quiz

**Q - Which join function might you use when you want rows in `x` that are not in `y`?**

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## Quiz

**Q - Which join function might you use when you want a dataset with all the columns from `x` and `y` and only the rows existing in both data frames?**

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## Quiz

**Q - Which join function might you use when you want rows in `x` that exist also in `y`?**

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# Questions?

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## Let's Practice Together!

Go to [AE 06: Data Wrangling 2](https://sta199-summer22.netlify.app/appex/ae06_BJ.html)

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## Bulletin

- Watch videos for [Prepare: May 20](https://sta199-summer22.netlify.app/prepare/week02_may20_BJ.html)

- Submit your `ae06`

- Lab 02 due Friday, May 20 at 11:59pm

- HW 01 due Tuesday, May 24 at 11:59pm