# Pipes and functions in R

## Learning objectives

* Demonstrate how to use the pipe
* Demonstrate piping alternatives
* Define functions and their purpose
* Analyze a user-written function and explain how it works
* Demonstrate conditional execution
* Practice writing functions

## Notes

**April 27, 2020**

## Pipes in R
* Think back to the `diamonds` dataset
* `filter()`, `group()`, and then `summarize()`

## Approaches to Coding

### Intermediate Steps
* `diamonds_# <- function`
* Unclear because the names are not intuitive
* Might forget what the name of the object means
* Make spelling mistakes
* Might start running out of memory (not as common)
* This works, but there are a couple of concerns when writing code this way **all the time**

### Overwrite the original

diamonds_t <- diamonds
diamonds_t <- filter()
...

* If something goes wrong, you basically have to start over adn retrieve the original dataset

### Function Composition

summarize(
  group_by(
    filter(diamonds, color == "I"),
    cut
  ),
  price = mean(price)
)

* Now we're writing code in sort of a backwards manner
* Again, **not very intuitive**

> All of these approaches produce the **exact same output**, but we want to make sure that our code is **interpretable** and **reproducible**_

### Piping
* A lot more intuitive
* Implicit
* Remember: You don't assign `<-` something to an object inside the pipe operator
* Depending on complexicity of task, you may have a lot of steps
* Break piped operation into a smaller set of tasks and save output
* Next line of code is **automaticaly indented** when you are using a piped operator
* For all of the `tidyverse` functions we use the `%>%` at the end of a line.
* `ggplot2` is different in that it uses a plus symbole `+`

> The `%>%` comes from the `maggritr` package. There are [other piping operators](https://r4ds.had.co.nz/pipes.html#other-tools-from-magrittr) in the package, including the "tee" pipe `%T%` and `%<>%`

## Functions in R
* Easy to use
* Self-documenting
* Easy-ier to debug
* **If you have copied and pasted a block of code more than twice, convert it to a function**

### Rescale Function
* Name
* Arguments
* Body

### How to use a function
* When using functions, by default the returned object is merely printed to the screen

## Conditional execution

if (condition) {
  # code executed when condition is TRUE
} else {
  # code executed when condition is FALSE
}

* Recoding variables is where you would use `if()` statements
* Need a **vectorized statement** check for multiple conditions
* `if_else()`

**FIZZBUZZ**