Data Wrangling 1

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# Data Wrangling 1
### Bora Jin

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<a href="https://introds.org" target="_blank">introds.org</a>
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## Material

🎥 Watch [Tidy Data](https://youtu.be/Ux85eR3h9hw)

- [Slides](https://rstudio-education.github.io/datascience-box/course-materials/slides/u2-d05-tidy-data/u2-d05-tidy-data.html#1)

🎥 Watch [Grammar of Data Wrangling](https://youtu.be/ZCaYBES_VEk)

- [Slides](https://rstudio-education.github.io/datascience-box/course-materials/slides/u2-d06-grammar-wrangle/u2-d06-grammar-wrangle.html#1)

🎥 Watch [Working With a Single Data Frame](https://youtu.be/0229Uq2hkJo)

- [Slides](https://rstudio-education.github.io/datascience-box/course-materials/slides/u2-d07-single-df/u2-d07-single-df.html#1)

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## Today's Goal

- Understand how data are organized according to a consistent set of "tidy" principles
- Use **seven key verbs** to wrangle data and extract meaning

"Happy families are all alike; every unhappy family is unhappy in its own way" - Leo Tolstoy

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## Quiz

Tidy data has three related characteristics

1. Each variable forms a column.
2. Each observation forms a row.
3. Each value has its own cell.

**Q - A tidy data set is tidy for any analyses (T/F).**

F
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## Quiz

**Q - What makes this data not tidy?**

<div class="figure" style="text-align: left">
<img src="img/05/untidy_data.png" alt="source: https://gist.github.com/Kimmirikwa/b69d0ea134820ea52f8481991ffae93e#file-student_results-csv" width="100%" />
<p class="caption">source: https://gist.github.com/Kimmirikwa/b69d0ea134820ea52f8481991ffae93e#file-student_results-csv</p>
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## Quiz

**Q - What makes this data not tidy?**

1. `sex and age`: multiple variables in one column
2. `test number`: not a value for each observation, `test 1` and `test 2` should be a variable 
3. `term 1-3`: can be aggregated

|id | name | phone | sex | age | test1 | test2 | term |
|:--|:-----|:------|:----|:----|:------|:------|:-----|
| 1 | Mike | 134   |  m  | 12  |  76   |  85   | term1|
| 1 | Mike | 134   |  m  | 12  |  84   |  80   | term2|
| 1 | Mike | 134   |  m  | 12  |  87   |  90   | term3|

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## Quiz

**Q - Correct the following sentences about** `dplyr` **functions:**

a. Its input can be a matrix.

b. Its output is in various forms.

c. Functions are nouns.

d. Replace the input data frame.

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## Quiz

**Q - Correct the following sentences about** `dplyr` **functions:**

a. Its input should be a **data frame**.

b. Its output is always a **data frame**.

c. Functions are **verbs**.

d. **Do not modify** the input data frame.

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## Quiz

**Q - Whic of these is the most appropriate translation of ** `%>%` **in English?**

a. Before

b. Which

c. Then

d. Do

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## Quiz

**Q - What of these is the most appropriate translation of ** `%>%` **in English?**

a. Before

b. Which

**c. Then**

d. Do

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## Quiz

**Q - Connect each function to its effect.**

.pull-left[
`filter` -

`arrange` -

`select` -

`distinct` -

`mutate` -

`summarize` -

`group_by` -

]

.pull-right[
- pick columns by variable names

- reorder rows by values of variables

- pick rows matching criteria

- enable grouped operations

- compute summary statistics

- extract unique rows

- create new variables

]

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## Quiz

**Q - Connect each function to its effect.**  <br>

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# Questions?

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## Let's Practice Together!

Go to [AE 05: Data Wrangling 1](https://sta199-summer22.netlify.app/appex/ae05_BJ.html)

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## Bulletin

- Watch videos for [Prepare: May 18](https://sta199-summer22.netlify.app/prepare/week02_may18_BJ.html)

- Make sure you commit **at least 3 times** for AEs

- Cannot give full credit for fewer than 3 commits from `ae03`

- Submit your `ae04`

- Complete up to `filter()` in `ae05`

- HW 01 released

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## Updated Bulletin on May 18

- No prepare for May 19

- Submit your `ae05`