ETC5510: Introduction to Data Analysis

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# .monash-blue.outline-text[ETC5510: Introduction to Data Analysis]

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<h2 style="font-weight:900!important;">Functions</h2>

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Lecturer: *Nicholas Tierney & Stuart Lee*

Department of Econometrics and Business Statistics

<span><i class="fas  fa-envelope faa-float animated "></i></span>  ETC5510.Clayton-x@monash.edu

April 2020

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---
class: refresher
# Recap

- File Paths

---
class: transition
# Motivating Functions

---
# Remember web scraping?

---
# How many episodes in Stranger Things?

```r
st_episode <- 
  bow("https://www.imdb.com/title/tt4574334/") %>%
  scrape() %>%
  html_nodes(".np_right_arrow .bp_sub_heading") %>%
  html_text() %>%
  str_remove(" episodes") %>%
  as.numeric()

st_episode
## [1] 33
```

---
# How many episodes in Stranger Things? And Mindhunter?

```r
st_episode <- bow("https://www.imdb.com/title/tt4574334/") %>%
  scrape() %>%
  html_nodes(".np_right_arrow .bp_sub_heading") %>%
  html_text() %>%
  str_remove(" episodes") %>%
  as.numeric()
st_episode
## [1] 33

mh_episodes <- bow("https://www.imdb.com/title/tt4574334/") %>%
  scrape() %>%
  html_nodes(".np_right_arrow .bp_sub_heading") %>%
  html_text() %>%
  str_remove(" episodes") %>%
  as.numeric()
mh_episodes
## [1] 33
```

---
# Why functions?

- Automate common tasks in a power powerful and general way than copy-and-pasting:
    - Give a functions an evocative name that makes code easier to understand.
    - As requirements change, **you only need to update code in one place, instead of many**.
    - You eliminate the chance of making incidental mistakes when you copy and paste (i.e. updating a variable name in one place, but not in another).

---
# Why functions?

- Down the line: Improve your reach as a data scientist by writing functions (and packages!) that others use

---
# Setup

```r
library(tidyverse)
library(rvest)
library(polite)

st <- bow("http://www.imdb.com/title/tt4574334/") %>% scrape()

twd <- bow("http://www.imdb.com/title/tt1520211/") %>% scrape()

got <- bow("http://www.imdb.com/title/tt0944947/") %>% scrape()
```

---
# When should you write a function?

Whenever you’ve copied and pasted a block of code more than twice.

When you want to clearly express some set of actions

(there are many other reasons as well!)

---
# Do you see any problems in the code below?

```r
st_episode <- st %>%
  html_nodes(".np_right_arrow .bp_sub_heading") %>%
  html_text() %>%
  str_replace(" episodes", "") %>%
  as.numeric()

got_episode <- got %>%
  html_nodes(".np_right_arrow .bp_sub_heading") %>%
  html_text() %>%
  str_replace(" episodes", "") %>%
  as.numeric()

twd_episode <- got %>%
  html_nodes(".np_right_arrow .bp_sub_heading") %>%
  html_text() %>%
  str_replace(" episodes", "") %>%
  as.numeric()
```

---
# Inputs

How many inputs does the following code have?

```r
st_episode <- st %>%
  html_nodes(".np_right_arrow .bp_sub_heading") %>%
  html_text() %>%
  str_replace(" episodes", "") %>%
  as.numeric()
```

---
# Turn the code into a function

Pick a short but informative **name**, preferably a verb.

```r
scrape_episode <- 
  
  
  
  
  
  
```

---
# Turn your code into a function

- Pick a short but informative **name**, preferably a verb.
- List inputs, or **arguments**, to the function inside `function`. If we had more the call would look like `function(x, y, z)`.

<br>

```r
scrape_episode <- function(x){
  
  
  
  
  
}  
```

---
# Turn your code into a function

- Pick a short but informative **name**, preferably a verb.
- List inputs, or **arguments**, to the function inside `function`. If we had more the call would look like `function(x, y, z)`.
- Place the **code** you have developed in body of the function, a `{` block that immediately follows `function(...)`.

```r
scrape_episode <- function(x){
  x %>%
    html_nodes(".np_right_arrow .bp_sub_heading") %>%
    html_text() %>%
    str_replace(" episodes", "") %>%
    as.numeric()
}
```

---
# Turn your code into a function

```r
scrape_episode <- function(x){
  x %>%
    html_nodes(".np_right_arrow .bp_sub_heading") %>%
    html_text() %>%
    str_replace(" episodes", "") %>%
    as.numeric()
}
```

```r
scrape_episode(st)
## [1] 33
```

---
# Check your function

- Number of episodes in The Walking Dead

```r
scrape_episode(twd)
## [1] 148
```

- Number of episodes in Game of Thrones

```r
scrape_episode(got)
## [1] 73
```

---
# Naming functions (it's hard)

> "There are only two hard things in Computer Science: cache invalidation and naming things." - Phil Karlton

- Names should be short but clearly evoke what the function does

- Names should be verbs, not nouns

- Multi-word names should be separated by underscores (`snake_case` as opposed to `camelCase`)

- A family of functions should be named similarly (`scrape_title`, `scrape_episode`, `scrape_genre`, etc.)

- Avoid overwriting existing (especially widely used) functions (e.g., `ggplot`)

---
# Scraping show info

```r
scrape_show_info <- function(x){

title <- x %>%
    html_node("#title-overview-widget h1") %>%
    html_text() %>%
    str_trim()

runtime <- x %>%
    html_node("time") %>%
    html_text() %>%
    str_replace("\\n", "") %>%
    str_trim()
  
  genres <- x %>%
    html_nodes(".txt-block~ .canwrap a") %>%
    html_text() %>%
    str_trim() %>%
    paste(collapse = ", ")
  
  tibble(title = title, runtime = runtime, genres = genres)
}
```

---
# Scraping show info

```r
scrape_show_info(st)
## # A tibble: 1 x 3
##   title           runtime genres                                           
##   <chr>           <chr>   <chr>                                            
## 1 Stranger Things 51min   Drama, Fantasy, Horror, Mystery, Sci-Fi, Thriller
scrape_show_info(twd)
## # A tibble: 1 x 3
##   title            runtime genres                 
##   <chr>            <chr>   <chr>                  
## 1 The Walking Dead 44min   Drama, Horror, Thriller
```

---
# How to update this function to use page URL as argument?

```r
scrape_show_info <- function(x){

title <- x %>% html_node("#title-overview-widget h1") %>%
    html_text() %>%
    str_trim()

runtime <- x %>% html_node("time") %>%
    html_text() %>%
    str_replace("\\n", "") %>%
    str_trim()
  
  genres <- x %>% html_nodes(".txt-block~ .canwrap a") %>%
    html_text() %>%
    str_trim() %>%
    paste(collapse = ", ")
  
  tibble(title = title, runtime = runtime, genres = genres)
}
```

---
# How to update this function to use page URL as argument?

```r
scrape_show_info <- function(x){
  
y <- bow(x) %>% scrape()

title <- y %>% html_node("#title-overview-widget h1") %>%
    html_text() %>%
    str_trim()

runtime <- y %>% html_node("time") %>%
    html_text() %>%
    str_replace("\\n", "") %>%
    str_trim()

genres <- y %>% html_nodes(".txt-block~ .canwrap a") %>%
    html_text() %>%
    str_trim() %>%
    paste(collapse = ", ")
  
  tibble(title = title, runtime = runtime, genres = genres)
}
```

---
# Let's check

```r
st_url <- "http://www.imdb.com/title/tt4574334/"
twd_url <- "http://www.imdb.com/title/tt1520211/"
```
--

```r
scrape_show_info(st_url)
## # A tibble: 1 x 3
##   title           runtime genres                                           
##   <chr>           <chr>   <chr>                                            
## 1 Stranger Things 51min   Drama, Fantasy, Horror, Mystery, Sci-Fi, Thriller
scrape_show_info(twd_url)
## # A tibble: 1 x 3
##   title            runtime genres                 
##   <chr>            <chr>   <chr>                  
## 1 The Walking Dead 44min   Drama, Horror, Thriller
```

---
class: transition

# Automation

---
# Automation

- You now have a function that will scrape the relevant info on shows given its URL. 
- Where can we get a list of URLs of top 100 most popular TV shows on IMDB? 
- Write the code for doing this in your teams.

---
# Automation

```r
urls <- bow("http://www.imdb.com/chart/tvmeter") %>%
  scrape() %>%
  html_nodes(".titleColumn a") %>%
  html_attr("href") %>%
  paste("http://www.imdb.com", ., sep = "")
```

```
##   [1] "http://www.imdb.com/title/tt6468322/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_1"  
##   [2] "http://www.imdb.com/title/tt5071412/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_2"  
##   [3] "http://www.imdb.com/title/tt3032476/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_3"  
##   [4] "http://www.imdb.com/title/tt10293938/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_4" 
##   [5] "http://www.imdb.com/title/tt6040674/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_5"  
##   [6] "http://www.imdb.com/title/tt0475784/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_6"  
##   [7] "http://www.imdb.com/title/tt1439629/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_7"  
##   [8] "http://www.imdb.com/title/tt12004280/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_8" 
##   [9] "http://www.imdb.com/title/tt3502248/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_9"  
##  [10] "http://www.imdb.com/title/tt0944947/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_10" 
##  [11] "http://www.imdb.com/title/tt0903747/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_11" 
##  [12] "http://www.imdb.com/title/tt1520211/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_12" 
##  [13] "http://www.imdb.com/title/tt1796960/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_13" 
##  [14] "http://www.imdb.com/title/tt2442560/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_14" 
##  [15] "http://www.imdb.com/title/tt0386676/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_15" 
##  [16] "http://www.imdb.com/title/tt9827854/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_16" 
##  [17] "http://www.imdb.com/title/tt7016936/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_17" 
##  [18] "http://www.imdb.com/title/tt8111088/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_18" 
##  [19] "http://www.imdb.com/title/tt8089592/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_19" 
##  [20] "http://www.imdb.com/title/tt9815454/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_20" 
##  [21] "http://www.imdb.com/title/tt0413573/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_21" 
##  [22] "http://www.imdb.com/title/tt3006802/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_22" 
##  [23] "http://www.imdb.com/title/tt2467372/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_23" 
##  [24] "http://www.imdb.com/title/tt0458290/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_24" 
##  [25] "http://www.imdb.com/title/tt2306299/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_25" 
##  [26] "http://www.imdb.com/title/tt8134186/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_26" 
##  [27] "http://www.imdb.com/title/tt8420184/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_27" 
##  [28] "http://www.imdb.com/title/tt4574334/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_28" 
##  [29] "http://www.imdb.com/title/tt10311562/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_29"
##  [30] "http://www.imdb.com/title/tt11823076/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_30"
##  [31] "http://www.imdb.com/title/tt11639414/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_31"
##  [32] "http://www.imdb.com/title/tt3526078/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_32" 
##  [33] "http://www.imdb.com/title/tt0460681/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_33" 
##  [34] "http://www.imdb.com/title/tt2741602/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_34" 
##  [35] "http://www.imdb.com/title/tt4565380/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_35" 
##  [36] "http://www.imdb.com/title/tt8398600/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_36" 
##  [37] "http://www.imdb.com/title/tt9244556/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_37" 
##  [38] "http://www.imdb.com/title/tt0108778/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_38" 
##  [39] "http://www.imdb.com/title/tt4179452/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_39" 
##  [40] "http://www.imdb.com/title/tt0306414/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_40" 
##  [41] "http://www.imdb.com/title/tt0141842/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_41" 
##  [42] "http://www.imdb.com/title/tt0452046/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_42" 
##  [43] "http://www.imdb.com/title/tt5753856/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_43" 
##  [44] "http://www.imdb.com/title/tt7661390/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_44" 
##  [45] "http://www.imdb.com/title/tt4052886/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_45" 
##  [46] "http://www.imdb.com/title/tt0455275/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_46" 
##  [47] "http://www.imdb.com/title/tt2085059/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_47" 
##  [48] "http://www.imdb.com/title/tt3107288/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_48" 
##  [49] "http://www.imdb.com/title/tt0203259/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_49" 
##  [50] "http://www.imdb.com/title/tt7908628/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_50" 
##  [51] "http://www.imdb.com/title/tt2802850/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_51" 
##  [52] "http://www.imdb.com/title/tt5420376/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_52" 
##  [53] "http://www.imdb.com/title/tt5180504/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_53" 
##  [54] "http://www.imdb.com/title/tt8741290/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_54" 
##  [55] "http://www.imdb.com/title/tt2304589/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_55" 
##  [56] "http://www.imdb.com/title/tt0364845/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_56" 
##  [57] "http://www.imdb.com/title/tt2661044/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_57" 
##  [58] "http://www.imdb.com/title/tt9642982/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_58" 
##  [59] "http://www.imdb.com/title/tt0804503/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_59" 
##  [60] "http://www.imdb.com/title/tt5834204/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_60" 
##  [61] "http://www.imdb.com/title/tt7366338/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_61" 
##  [62] "http://www.imdb.com/title/tt7414406/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_62" 
##  [63] "http://www.imdb.com/title/tt1405406/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_63" 
##  [64] "http://www.imdb.com/title/tt0898266/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_64" 
##  [65] "http://www.imdb.com/title/tt0411008/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_65" 
##  [66] "http://www.imdb.com/title/tt1844624/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_66" 
##  [67] "http://www.imdb.com/title/tt1586680/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_67" 
##  [68] "http://www.imdb.com/title/tt3205802/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_68" 
##  [69] "http://www.imdb.com/title/tt1266020/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_69" 
##  [70] "http://www.imdb.com/title/tt1632701/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_70" 
##  [71] "http://www.imdb.com/title/tt1124373/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_71" 
##  [72] "http://www.imdb.com/title/tt7767422/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_72" 
##  [73] "http://www.imdb.com/title/tt2356777/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_73" 
##  [74] "http://www.imdb.com/title/tt7134908/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_74" 
##  [75] "http://www.imdb.com/title/tt8045468/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_75" 
##  [76] "http://www.imdb.com/title/tt0491738/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_76" 
##  [77] "http://www.imdb.com/title/tt4524056/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_77" 
##  [78] "http://www.imdb.com/title/tt1475582/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_78" 
##  [79] "http://www.imdb.com/title/tt0407362/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_79" 
##  [80] "http://www.imdb.com/title/tt10361016/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_80"
##  [81] "http://www.imdb.com/title/tt4786824/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_81" 
##  [82] "http://www.imdb.com/title/tt1190634/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_82" 
##  [83] "http://www.imdb.com/title/tt0460649/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_83" 
##  [84] "http://www.imdb.com/title/tt9308346/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_84" 
##  [85] "http://www.imdb.com/title/tt3920596/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_85" 
##  [86] "http://www.imdb.com/title/tt2805096/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_86" 
##  [87] "http://www.imdb.com/title/tt1442437/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_87" 
##  [88] "http://www.imdb.com/title/tt9073958/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_88" 
##  [89] "http://www.imdb.com/title/tt10314462/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_89"
##  [90] "http://www.imdb.com/title/tt7456722/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_90" 
##  [91] "http://www.imdb.com/title/tt2861424/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_91" 
##  [92] "http://www.imdb.com/title/tt2707408/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_92" 
##  [93] "http://www.imdb.com/title/tt0412142/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_93" 
##  [94] "http://www.imdb.com/title/tt8806524/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_94" 
##  [95] "http://www.imdb.com/title/tt7660850/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_95" 
##  [96] "http://www.imdb.com/title/tt0096697/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_96" 
##  [97] "http://www.imdb.com/title/tt2261391/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_97" 
##  [98] "http://www.imdb.com/title/tt4158110/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_98" 
##  [99] "http://www.imdb.com/title/tt8550800/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_99" 
## [100] "http://www.imdb.com/title/tt2193021/?pf_rd_m=A2FGELUUNOQJNL&pf_rd_p=332cb927-0342-42b3-815c-f9124e84021d&pf_rd_r=75PKE0301CECR4D4KX47&pf_rd_s=center-1&pf_rd_t=15506&pf_rd_i=tvmeter&ref_=chttvm_tt_100"
```

---
# Automation: Go to each page, scrape show info

- Programatically direct R to each page on the `urls` list and run  `scrape_show_info`

```r
scrape_show_info(urls[1])
## # A tibble: 1 x 3
##   title       runtime  genres
##   <chr>       <chr>    <chr> 
## 1 Money Heist 1h 10min ""
scrape_show_info(urls[2])
## # A tibble: 1 x 3
##   title runtime genres                
##   <chr> <chr>   <chr>                 
## 1 Ozark 1h      Crime, Drama, Thriller
scrape_show_info(urls[3])
## # A tibble: 1 x 3
##   title            runtime genres      
##   <chr>            <chr>   <chr>       
## 1 Better Call Saul 46min   Crime, Drama
```

---
# Go to each page, scrape show info

In other words, we want to **map** the `scrape_show_info` function to each element of `show_urls`:

```r
top_100_shows <- map_df(urls, scrape_show_info)
```

- This will hit the `urls` one after another, and grab the info.

---
# Passing functions to ... functions?

- The fact that we can pass a function to another is a **big idea**, and is one of the things that makes R a **functional programming language**.
- It's a bit mind-bending, but it's an idea worth practicing and comfortable with

---
# aside: `list`s as an idea: first...vectors

- `c()` creates a **vector** of one type
- e.g., `x <- c(1, 2, 3, "A")` contains:
- `[1] "1" "2" "3" "A"` 
- `class(x)` returns:
- `[1] "character"`

---
# aside: `list`s as an idea: first...vectors

- You can look up vectors based on position with `[]`
- `x[1]` returns the first thing
- `x[2]` returns the second thing
- `x[1:2]` returns the first through to second thing

---
# aside: `list`s as an idea: second...lists

- `list()` creates list, which can be any type

```r
y <- list(1,2,3,"x"); y
#> [[1]]
#> [1] 1
#> 
#> [[2]]
#> [1] 2
#> 
#> [[3]]
#> [1] 3
#> 
#> [[4]]
#> [1] "x"
```

---
# aside: `list`s as an idea: second...lists

- You access positions of a list with `[[]]`
- So `y[[1]]` returns: `1`

---
# aside: a `data frame` is actually a list!

---
# calculate the mean for every column:

```r
map(mtcars, mean)
## $mpg
## [1] 20.09062
## 
## $cyl
## [1] 6.1875
## 
## $disp
## [1] 230.7219
## 
## $hp
## [1] 146.6875
## 
## $drat
## [1] 3.596563
## 
## $wt
## [1] 3.21725
## 
## $qsec
## [1] 17.84875
## 
## $vs
## [1] 0.4375
## 
## $am
## [1] 0.40625
## 
## $gear
## [1] 3.6875
## 
## $carb
## [1] 2.8125
```

---
# calculate the mean for every column:

```r
map_dbl(mtcars, mean)
##        mpg        cyl       disp         hp       drat         wt       qsec 
##  20.090625   6.187500 230.721875 146.687500   3.596563   3.217250  17.848750 
##         vs         am       gear       carb 
##   0.437500   0.406250   3.687500   2.812500
```

---
# Range for every column: writing a function

```r
my_range <- function(x){
  max(x) - min(x)
}
map_dbl(mtcars, my_range)
##     mpg     cyl    disp      hp    drat      wt    qsec      vs      am    gear 
##  23.500   4.000 400.900 283.000   2.170   3.911   8.400   1.000   1.000   2.000 
##    carb 
##   7.000
```

---
# Range for every column: writing a function in map

```r
map_dbl(mtcars, .f = function(x) max(x) - min(x))
##     mpg     cyl    disp      hp    drat      wt    qsec      vs      am    gear 
##  23.500   4.000 400.900 283.000   2.170   3.911   8.400   1.000   1.000   2.000 
##    carb 
##   7.000
```

---
# Range for every column: writing a function in map

```r
map_dbl(mtcars, .f = ~(max(.) - min(.)))
##     mpg     cyl    disp      hp    drat      wt    qsec      vs      am    gear 
##  23.500   4.000 400.900 283.000   2.170   3.911   8.400   1.000   1.000   2.000 
##    carb 
##   7.000
```

---
# Your Turn!

Take the lab quiz!

---
# Resources

- Jenny Bryans blog post
- functions chapter of r4DS
- iteration section of r4ds
- [lists section in advanced R](https://adv-r.hadley.nz/vectors-chap.html#lists)