10,000 Reasons to Love Functions

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background-image: url(https://source.unsplash.com/jiUNAQb6Cfk/1600x900)
background-size: cover

# .purple[10,000 Reasons to Love Functions]

## .gray[Garrick Aden-Buie]

---
exclude: true

1. Farkle, rules and example
1. Declarative programming
1. Refactor into a function... what is a function?
1. Functions reduce copy/paste
1. Functions encapsulate logic
 - Declare assumptions
1. Functions simplify logic
1. Functions can be **composed** (`magrittr`, `purrr`)
1. Functions can be **parallel** (`furrr`)
1. Functions can be packaged (`usethis`)
1. Functions can be tested (`testthat`)
1. Functions can be debugged
1. Functions can be modified
1. Functions can be documented (`roxygen2`)
1. Documentation can be beautiful (`pkgdown`)
1. Functions can be coordinated (`drake`)

---
class: fullscreen
background-image: url(assets/img/farkle.jpg)
background-size: contain

---
layout: true

# Farkle Rules

.w-50.h-100.fl.mt3.pr4[
![](assets/img/farkle-rules.jpg)
]

---

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 <thead class="gt_col_headings">
 <tr>
 <th class="gt_col_heading gt_columns_bottom_border gt_left" rowspan="1" colspan="1">Combination</th>
 <th class="gt_col_heading gt_columns_bottom_border gt_left" rowspan="1" colspan="1">Score</th>
 </tr>
 </thead>
 <tbody class="gt_table_body">
 <tr>
 <td class="gt_row gt_left">Single 5</td>
 <td class="gt_row gt_left">50</td>
 </tr>
 <tr>
 <td class="gt_row gt_left">Single 1</td>
 <td class="gt_row gt_left">100</td>
 </tr>
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 <td class="gt_row gt_left">3 x N of a kind</td>
 <td class="gt_row gt_left">N * 100</td>
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 <td class="gt_row gt_left">(n - 3) * 1000</td>
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 <td class="gt_row gt_left">3 Pairs</td>
 <td class="gt_row gt_left">1500</td>
 </tr>
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 <td class="gt_row gt_left">Straight</td>
 <td class="gt_row gt_left">1500</td>
 </tr>
 <tr>
 <td class="gt_row gt_left">2 Triplets</td>
 <td class="gt_row gt_left">2500</td>
 </tr>
 </tbody>
 
 
</table></div>
]

---

.w-50.fr.f7[
You rolled...

]

.w-50.fr.f7[
- 







 = 400

- 

 = 100

- 




 = 50 x 2
]

.w-50.fr.f7[
And you get to roll again
]

---

.w-50.fr.f7[
Score: **600**. On your next roll...

]

.w-50.fr.f7[
You can choose one or both of

- 

 = 100

- 

 = 50
]

.w-50.fr.f7[
Pick the 

, roll **5** dice
]

---

.w-50.fr.f7[
Current Score: **700**

]

.w-50.fr.f7[
You can choose one or both of

- 

 = 50

- 

 = 50
]

.w-50.fr.f7[
Pick both 

, roll **3** dice
]

---

.w-50.fr.f7[
Current Score: **800**
]

.w-50.fr.f7[









]

.w-50.fr.f7[
.red.b[FARKLE! &#x1F622;]

Final Score: ~~800~~
]

---
layout: true

# How to roll computer dice

---

```r
n_dice_to_roll <- 6
dice_values <- 1:6
sample(dice_values, size = n_dice_to_roll, replace = FALSE)
```

```
## [1] 5 3 1 2 4 6
```

```r
*roll_dice <- function(n_dice_to_roll) {
 dice_values <- 1:6
 sample(dice_values, size = n_dice_to_roll, replace = FALSE)
*} 
```

```r
roll_dice(6)
```

```
## [1] 1 2 5 6 3 4
```

---

```r
roll_dice <- function(n) {
 sample(1:6, size = n, replace = FALSE)
}
```

```r
(dice_rolled <- roll_dice(6))
```

```
## [1] 4 3 2 6 5 1
```

```r
html_dice(dice_rolled, size = "3x")
```

---

```r
lapply(1:5, function(...) roll_dice(n = 6))
```

```
## [[1]]
## [1] 1 3 5 6 2 4
## 
## [[2]]
## [1] 3 5 1 2 4 6
## 
## [[3]]
## [1] 2 3 4 1 6 5
## 
## [[4]]
## [1] 2 6 4 5 1 3
## 
## [[5]]
## [1] 5 1 2 4 3 6
```

---

```r
roll_dice <- function(n) {
* sample(1:6, size = n, replace = TRUE)
}
```

```r
html_dice(roll_dice(6), size = "3x")
```

```r
html_dice(roll_dice(6), size = "3x")
```

---

```r
lapply(1:5, function(...) roll_dice(n = 6))
```

```
## [[1]]
## [1] 3 1 2 3 5 3
## 
## [[2]]
## [1] 3 1 6 5 4 1
## 
## [[3]]
## [1] 1 1 6 5 5 3
## 
## [[4]]
## [1] 5 1 1 6 2 6
## 
## [[5]]
## [1] 2 2 3 5 4 1
```

---
layout: true

# Anatomy of a Function

.f5.mt5[
```
roll_dice <- function(n) {
 sample(1:6, size = n, replace = TRUE)
}
```
]

---

---
background-image: url(assets/img/function-anatomy-3.jpg)
background-size: cover

---
background-image: url(assets/img/function-anatomy-4.jpg)
background-size: cover

---
background-image: url(assets/img/function-anatomy-5.jpg)
background-size: cover

---
layout: true

# Anatomy of a Function

---

.f5[

```r
roll_dice <- function(n) {
* if (n > 6) {
* stop("Can't roll more than 6 dice")
* }
 sample(1:6, size = n, replace = TRUE)
}
```
]

---

.f5[

```r
roll_dice <- function(n) {
 if (n > 6) {
 stop("Can't roll more than 6 dice")
 }
* if (n < 1) {
* stop("Must roll at least 1 die")
* }
 sample(1:6, size = n, replace = TRUE)
}
```
]

---
layout: false
class: break center middle break-blue-pink

# A Farkle Roll

.w-50.f6.mh-auto.tl[
- Roll the dice in your hand
]
--

.w-50.f6.mh-auto.tl[
- Count the dice you rolled
]
--

.w-50.f6.mh-auto.tl[
- Score the dice combinations
]
--

.w-50.f6.mh-auto.tl[
- Choose which dice to keep and which dice to re-roll
]

---

# Roll the dice in your hand

```r
set.seed(2020-05+15)
dice_rolled <- roll_dice(6)
```

```r
html_dice(dice_rolled, "3x")
```

---
layout: true

# Count the dice you rolled

```r
library(dplyr, warn.conflicts = FALSE)
tibble(value = dice_rolled) %>% count(value)
```

---

```
## # A tibble: 3 x 2
## value n
## <int> <int>
## 1 1 2
## 2 2 3
## 3 4 1
```

---

```r
count_dice <- function(dice) {
 dplyr::tibble(value = dice) %>% dplyr::count(value)
}
```

```r
(dice_counted <- count_dice(dice_rolled))
```

```
## # A tibble: 3 x 2
## value n
## <int> <int>
## 1 1 2
## 2 2 3
## 3 4 1
```

---
layout: false

# Score the dice combinations

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}

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  text-transform: inherit;
  padding-top: 8px;
  padding-bottom: 8px;
  padding-left: 5px;
  padding-right: 5px;
}

#cjzdiluzfi .gt_first_summary_row {
  padding-top: 8px;
  padding-bottom: 8px;
  padding-left: 5px;
  padding-right: 5px;
  border-top-style: solid;
  border-top-width: 2px;
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}

#cjzdiluzfi .gt_grand_summary_row {
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  background-color: #FFFFFF;
  text-transform: inherit;
  padding-top: 8px;
  padding-bottom: 8px;
  padding-left: 5px;
  padding-right: 5px;
}

#cjzdiluzfi .gt_first_grand_summary_row {
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  padding-left: 5px;
  padding-right: 5px;
  border-top-style: double;
  border-top-width: 6px;
  border-top-color: #D3D3D3;
}

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  border-top-width: 2px;
  border-top-color: #D3D3D3;
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  border-bottom-width: 2px;
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}

#cjzdiluzfi .gt_footnotes {
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  border-bottom-width: 2px;
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  border-right-width: 2px;
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}

#cjzdiluzfi .gt_footnote {
  margin: 0px;
  font-size: 90%;
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}

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}

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  font-size: 90%;
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}

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 font-style: italic;
 font-size: 65%;
}
</style>
<div id="cjzdiluzfi" style="overflow-x:auto;overflow-y:auto;width:auto;height:auto;"><table class="gt_table">
 
 <thead class="gt_col_headings">
 <tr>
 <th class="gt_col_heading gt_columns_bottom_border gt_left" rowspan="1" colspan="1">Combination</th>
 <th class="gt_col_heading gt_columns_bottom_border gt_left" rowspan="1" colspan="1">Score</th>
 </tr>
 </thead>
 <tbody class="gt_table_body">
 <tr>
 <td class="gt_row gt_left">2 Triplets</td>
 <td class="gt_row gt_left">2500</td>
 </tr>
 <tr>
 <td class="gt_row gt_left">Straight</td>
 <td class="gt_row gt_left">1500</td>
 </tr>
 <tr>
 <td class="gt_row gt_left">3 Pairs</td>
 <td class="gt_row gt_left">1500</td>
 </tr>
 <tr>
 <td class="gt_row gt_left">4:6 of a Kind</td>
 <td class="gt_row gt_left">(n - 3) * 1000</td>
 </tr>
 <tr>
 <td class="gt_row gt_left">3 x N of a kind</td>
 <td class="gt_row gt_left">N * 100</td>
 </tr>
 <tr>
 <td class="gt_row gt_left">Single 1</td>
 <td class="gt_row gt_left">100</td>
 </tr>
 <tr>
 <td class="gt_row gt_left">Single 5</td>
 <td class="gt_row gt_left">50</td>
 </tr>
 </tbody>
 
 
</table></div>
]

.w-two-thirds.fr.pl3[
- Check if we have the combination

- Identify the dice used

- Score the dice combination

- Remove dice used from future scoring
]

.w-two-thirds.fr[

```r
dice_rolled_ex <- 1:6
dice_counted_ex <- count_dice(dice_rolled_ex)

if (identical(dice_counted_ex$value, 1:6)) {
 score <- 1500
 dice_counted_ex$n <- 0
}
```
]

---
layout: true

# Score 3 of a Kind

.w-30.fl.pr2[
- Check for combo

- Identify dice

- Score combination

- Remove dice

```r
dice_counted
```

```
## # A tibble: 3 x 2
## value n
## <int> <int>
## 1 1 2
## 2 2 3
## 3 4 1
```

]

---

.w-70.fr.can-edit[

```r
# Pseudo-code is okay
if (condition) {
  
}
```
]

---

.w-70.fr[

```r
dice_counts <- dice_counted$n
dice_values <- dice_counted$value

*if (any(dice_counts == 3)) {
* # 3 of a kind
* for (used in which(dice_counts == 3)) {
* value <- dice_values[used]
* # three ones is 300
* if (value == 1) value <- 3
* score <- value * 100
* dice_counts[used] <- 0
* }
*} 
```
]

---
layout: true
class: last-output-only

# Score 3 of a Kind with Functions

---

```r
has_3_of_kind <- function(dice_counted) {
 if (sum(dice_counted$n) < 3) return(FALSE)
 any(dice_counted$n == 3)
}

identify_3_of_kind <- function(dice_counted) {
 # get largest dice value first
 dice_counted %>%
 filter(n == 3) %>%
 tail(n = 1) %>%
 transmute(value, use = 3)
}

score_3_of_kind <- function(dice_identified) {
 tibble(used = 3, score = dice_identified$value * 100)
}
```

---

```r
*has_3_of_kind <- function(dice_counted) {
 if (sum(dice_counted$n) < 3) return(FALSE)
 any(dice_counted$n == 3)
}

*identify_3_of_kind <- function(dice_counted) {
 # get largest dice value first
 dice_counted %>%
 filter(n == 3) %>%
 tail(n = 1) %>%
 transmute(value, use = 3)
}

*score_3_of_kind <- function(dice_identified) {
 value <- dice_identified$value
 tibble(used = 3, score = ifelse(value ==1, 3, value) * 100)
}
```

---

```r
dice_counted
```

```
## # A tibble: 3 x 2
## value n
## <int> <int>
## 1 1 2
## 2 2 3
## 3 4 1
```

```r
has_3_of_kind(dice_counted)
```

```
## [1] TRUE
```

```r
(dice_used <- identify_3_of_kind(dice_counted))
```

```
## # A tibble: 1 x 2
## value use
## <int> <dbl>
## 1 2 3
```

```r
(combo_score <- score_3_of_kind(dice_used))
```

```
## # A tibble: 1 x 2
## used score
## <dbl> <dbl>
## 1 3 200
```

---

.flex[
.w-50.pr4[

```r
dice_counted
```

```
## # A tibble: 3 x 2
## value n
## <int> <int>
## 1 1 2
## 2 2 3
## 3 4 1
```
]
.w-50[

```r
dice_used
```

```
## # A tibble: 1 x 2
## value use
## <int> <dbl>
## 1 2 3
```

]
]

```r
use_dice <- function(dice_counted, dice_used) {
 left_join(dice_counted, dice_used, by = "value") %>%
 mutate(use = ifelse(is.na(use), 0, use)) %>%
 transmute(value, n = n - use) %>%
 filter(n > 0)
}
```

---

.flex[
.w-third.pr1[

```r
dice_counted
```

```
## # A tibble: 3 x 2
## value n
## <int> <int>
## 1 1 2
## 2 2 3
## 3 4 1
```
]
.w-third.pr1[

```r
dice_used
```

```
## # A tibble: 1 x 2
## value use
## <int> <dbl>
## 1 2 3
```
]
.w-third[

```r
combo_score
```

```
## # A tibble: 1 x 2
## used score
## <dbl> <dbl>
## 1 3 200
```
]
]

.dummy[

```r
(dice_left <- use_dice(dice_counted, dice_used))
```

```
## # A tibble: 2 x 2
## value n
## <int> <dbl>
## 1 1 2
## 2 4 1
```
]

---
layout: false

# Score a Roll

```r
score_roll <- function(dice) {
 n_dice <- length(dice)
 dice_counted <- count_dice(dice)
 
 score_combos <- NULL
 
 # ... check for high points first ...
 
 if (has_3_of_kind(dice_counted)) {
 dice_used <- identify_3_of_kind(dice_counted)
 combo_score <- score_3_of_kind(dice_used)
 score_combos <- bind_rows(score, combo_score)
 dice_counted <- use_dice(dice_counted, dice_used)
 }
 
 # ... return score options ...
}
```

---

# When to use functions?

.w-80[
> You should consider writing a function whenever you’ve **copied and pasted** a block of code **more than twice** (i.e. you now have three copies of the same code).
> <cite>R for Data Science</cite>
]

.w-two-thirds.tr.fr[
> Sure, but functions are useful **even if you only call them once** 
> <cite>Me, right now</cite>
]

---
class: break bg-purple middle

# .white[A few reasons to love functions]

.absolute.bottom-0.right-1.white[
.f6[*]The exact moment when this talk went off the rails
]

---

# Functions can be **packaged**

.f5.code[
[usethis.r-lib.org](https://usethis.r-lib.org)
]

```r
usethis::create_package("farkle")
```

.absolute.bottom-1.right-1[
![](https://usethis.r-lib.org/reference/figures/logo.png)
]

---

# Functions can be **tested**

.f5.code[
[testthat.r-lib.org](https://testthat.r-lib.org)
]

```r
usethis::use_testthat()
# Open your R file
usethis::use_test()
```

.absolute.bottom-1.right-1[
![](https://testthat.r-lib.org/reference/figures/logo.png)
]

---

# Functions can be **debugged**

- Use your tests

- Use break points

- Use `debug()` or `debugOnce()`

- Use `options(error = recover)`

---

# Functions can be **modified**

- Use your tests as a safety net

- You know what .green.b[goes in] and what should .b.red[come out]

---

# Functions can be **documented**

.f5.code[
[roxygen2.r-lib.org](https://roxygen2.r-lib.org)
]

```r
#' Function Title
#' 
#' Function description (paragraph)
#' 
#' @param n Number of dice to roll
#' @export
roll_dice <- function(n) {
 # ...
}
```

.absolute.bottom-1.right-1[
![](https://roxygen2.r-lib.org/reference/figures/logo.png)
]

---

# Functions documentation can be **beautiful**

.f5.code[
[pkgdown.r-lib.org](https://pkgdown.r-lib.org)
]

```r
pkgdown::init_site()
pkgdown::build_site()
```

.absolute.bottom-1.right-1[
![](https://pkgdown.r-lib.org/reference/figures/logo.png)
]

---

# Functions can be tested, **continuously**

.f5.code[
[maxheld.de/ghactions](https://www.maxheld.de/ghactions/)
]

```r
ghactions::use_ghactions(workflow = ghactions::website())
```

.absolute.bottom-1.right-2.w-20[
![](https://raw.githubusercontent.com/maxheld83/ghactions/master/logo.png)
]

---

# Functions can be **coordinated**

.f5.code[
[docs.ropensci.org/drake](https://docs.ropensci.org/drake)
]

```r
drake::use_drake()
```

.absolute.bottom-1.right-2.w-20[
![](https://camo.githubusercontent.com/44749362ca36c9e3295f2bcf18975d811564c121/68747470733a2f2f646f63732e726f70656e7363692e6f72672f6472616b652f7265666572656e63652f666967757265732f6c6f676f2e737667)
]