Recap III

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# Recap III
### The R Bootcamp Twitter: <a href='https://twitter.com/therbootcamp'>@therbootcamp</a>
### April 2018

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# Tidying

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In this introduction you will learn...

>...more about R projects.
><br2>
>...how to write clean, documented code.
><br2>
>...to understand errors (and warnings).
><br2>
>...how to deal with missing values.
]

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<img src="https://build2be.com/sites/build2be.com/files/shutterstock_232639537.jpg" width="500">
source<a href="https://build2be.com/"> https://build2be.com/</a>
]

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# Style

Check out the [**Google's R style guide**](https://google.github.io/styleguide/Rguide.xml) & [**Tidyverse style guide**](http://style.tidyverse.org/index.html)

### Bad

```r
mean(subset((data.frame(c('a','b'),runif(1000,0,1))),c..a....b..=='a')[,'runif.1000..0..1.'])
```

### Good

```r
# create my data.frame
my_data <- data.frame('group' = c('a','b'), 
 'value' = runif(1000,0,1))

# subset data
my_data %>% 
  filter(group == 'a') %>%
  summarize(mean(value))
```

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# Project structure

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Good, clean, documented code begins with a **project** and a **folder structure**.
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<img src="https://raw.githubusercontent.com/therbootcamp/therbootcamp.github.io/master/_sessions/_image/folder_structure.png" width="400">
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# 7 most frequent errors

According to [stackoverflow.com](http://www.stackoverflow.com)

| Error| Example| Description|
|:------|:------------|:--------------------------------------------|
| `'could not find function'`|lenth(my_vec)| There is a typo in the function name or that a package has not been loaded.|
| `'error in if'`|if(NA == 2) 2 + 2| The object in the `if` clause is non-logical or NA.|
| `'error in eval'`|lm(fefq~wzfe)| An object is used that does not exist.|
| `'cannot open()'`|read_csv('hjht.txt')| The file does not exist. Could be a typo or a missing filepath.|
| `'no applicable method'`|predict('efwe')| A 'generic function' has not been defined for this type/class |
| `'subsscript out of bounds'`|a <- matrix(c(1,2)); a[2,2]| R tried to access an element (or variable) that does not exist |
| package errors|| Occur when R is unable to install, compile, or load a package. Often this means that some software background is missing. |

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# You can do amazing plots in R!

- As good as R is for statistics, it's as good if not better for plots.

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## ggplot2

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How do we make elegant, easy to program plots according to the grammar of graphics in R?

###Answer: ggplot2

By far one of the most popular R packages, used to generate the vast majority of plots from R.

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## Grammar of Graphics

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The Grammar of graphics breaks down plots into several key pieces:

| aesthetics| Description|
|:------|:----|
|     Data|    What dataframe contains the data?|
|     Aesthetics| What does the x-axis, y-axis, color (etc) represent?|
|     Geometries| What kind of geometric object do you want to plot?|
|     Facets| Should there be groups of plots?|
|     Statistics|What statistic summaries / transformations should be done?|
|    Coordinates| What is the scale of the axes?|
|    Theme| What should the overall plot look like?|

]

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## Final result!

```r
ggplot(data = mpg, 
       mapping = aes(x = displ, y = hwy, col = class)) +
  geom_point() + 
  geom_smooth(col = "blue", method = "lm")+
  labs(x = "Engine Displacement in Liters",
       y = "Highway miles per gallon",
       title = "MPG data",
       subtitle = "Cars with higher engine displacement tend to have lower highway mpg",
       caption = "Source: mpg data in ggplot2") + 
  theme_bw()
```

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# Caret

- Caret stands for Classification And REgression Training.

- Caret is data scientist's dream for conducting machine learning.

- No need to learn different functions or syntax for different models.

- `method = 'lm'` ...Regression!
    - `method = 'rm'` ...Random forests!

- Do very complex machine learning tasks with a few simple functions

]

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<div class="figure" style="text-align: center">
<img src="https://3qeqpr26caki16dnhd19sv6by6v-wpengine.netdna-ssl.com/wp-content/uploads/2014/09/Caret-package-in-R.png" alt="The almighty Caret!" width="90%" />
The almighty Caret!
</div>

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## What is Shiny?

<div class="figure" style="text-align: center">
<img src="https://github.com/therbootcamp/therbootcamp.github.io/blob/master/_sessions/_image/shiny_definition.png?raw=true" alt="Source: http://shiny.rstudio.com/images/shiny-cheatsheet.pdf" width="95%" />
Source: http://shiny.rstudio.com/images/shiny-cheatsheet.pdf
</div>

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# Today

<a href="https://therbootcamp.github.io/BaselRBootcamp_2018April/schedule">Schedule</a>