Writing Functions

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# Writing Functions
## Dr. Mine Dogucu
]

---

## Definining functions

```r
double <- function(number) {
  number*2
}
```

The name of the function is `double()` and it takes one argument `number`.

---

```r
double(number = 3)
```

```
## [1] 6
```

```r
double(3)
```

```
## [1] 6
```

---

## Setting a default argument

```r
double <- function(number = 5) {
  number*2
}
```

---

```r
double()
```

```
## [1] 10
```

---

## Having multiple arguments

```r
multiply <- function(number, by) {
  number*by
}
```

```r
multiply(number = 10, by = 3)
```

```
## [1] 30
```

---

## Goal

Can we get the top 50 highest ranked feature movies for any year?

---

[Featured Movies](https://www.imdb.com/search/title/?title_type=feature&year=2010-01-01,2010-12-31&sort=user_rating,desc)

---

## Scraping the 2010 movie titles

```r
library(tidyverse)
library(rvest)
page <- "https://www.imdb.com/search/title/?title_type=feature&year=2010-01-01,2010-12-31&sort=user_rating,desc"
read_html(page) %>% 
  html_nodes(".lister-item-header a") %>% 
  html_text()
```

```
##  [1] "Lebensraum/Living Space"                                                    
##  [2] "Revolver: Poor Boyz"                                                        
##  [3] "Bohlol Dana - A Sage of Baghdad"                                            
##  [4] "Tebaatusasula"                                                              
##  [5] "Townbiz"                                                                    
##  [6] "Die Haushaltshilfe"                                                         
##  [7] "Min pinlige familie og mutantdræbersneglene"                                
##  [8] "Dhinveynugehithaamaigaa"                                                    
##  [9] "It's Always Sunny in Philadelphia: Cast & Creators Live at the Paley Center"
## [10] "DranDeh"                                                                    
## [11] "Truth & Life Dramatized Audio Bible"                                        
## [12] "Les palmiers blessés"                                                       
## [13] "Staying Gold"                                                               
## [14] "Love Equation"                                                              
## [15] "The Final Journey"                                                          
## [16] "The Ballad of Frankie Silver"                                               
## [17] "Les Misérables in Concert: The 25th Anniversary"                            
## [18] "Doraleous and Associates"                                                   
## [19] "A3D Ayumi Hamasaki Arena Tour 2009 A: Next Level"                           
## [20] "Kisses, Chloe"                                                              
## [21] "Barriere"                                                                   
## [22] "Unbelehrbar"                                                                
## [23] "New Kids on the Block: Coming Home"                                         
## [24] "In Focus"                                                                   
## [25] "Inception"                                                                  
## [26] "Nobody Smiling"                                                             
## [27] "American Falls"                                                             
## [28] "The Clock"                                                                  
## [29] "Heroes Crossing"                                                            
## [30] "The Corners"                                                                
## [31] "The Toll"                                                                   
## [32] "Rat Rod Rockers!"                                                           
## [33] "Urban Wolf"                                                                 
## [34] "Grand Slammed"                                                              
## [35] "Jen"                                                                        
## [36] "Supériorité"                                                                
## [37] "The New Normal"                                                             
## [38] "Freedom Hills"                                                              
## [39] "Vecinos"                                                                    
## [40] "Sesame Street: C is for Cookie Monster"                                     
## [41] "Green Day: 21st Century Breakdown"                                          
## [42] "Life of the Party: Vol. II"                                                 
## [43] "National Theatre Live: Nation"                                              
## [44] "The Wizard of Agni"                                                         
## [45] "Slednecks 13"                                                               
## [46] "Writer's Block"                                                             
## [47] "Black Eyed Peas 3D: Live"                                                   
## [48] "Step Away from the Stone"                                                   
## [49] "The Beekeepers"                                                             
## [50] "Out of Focus"
```

---

## Scraping the 2011 movie titles

```r
page <- "https://www.imdb.com/search/title/?title_type=feature&year=2011-01-01,2011-12-31&sort=user_rating,desc"
read_html(page) %>% 
  html_nodes(".lister-item-header a") %>% 
  html_text()
```

```
##  [1] "Ashi Fasli Nanachi Tang"                                                 
##  [2] "Imported Affairs"                                                        
##  [3] "Deswa"                                                                   
##  [4] "Ka Oryang"                                                               
##  [5] "Year of the Rat"                                                         
##  [6] "Love on a Leash"                                                         
##  [7] "Losers in Love"                                                          
##  [8] "The Script: Homecoming"                                                  
##  [9] "Rescue Team"                                                             
## [10] "Howling at the Moon"                                                     
## [11] "Sans pudeur ni morale"                                                   
## [12] "Kill Bill: The Whole Bloody Affair"                                      
## [13] "Virtual Trek Wildlife Park"                                              
## [14] "The Nutcracker and the Mouse King"                                       
## [15] "Flashback"                                                               
## [16] "Myth & Mystery"                                                          
## [17] "American Actor"                                                          
## [18] "Blood Eclipse"                                                           
## [19] "So Much Pain So in Love"                                                 
## [20] "The Phantom of the Opera at the Royal Albert Hall"                       
## [21] "The Second Times of Troubles"                                            
## [22] "At the Jersey Shore"                                                     
## [23] "Stalemate"                                                               
## [24] "Gente mala del norte"                                                    
## [25] "Mr. Plinkett's Indiana Jones and the Kingdom of the Crystal Skull Review"
## [26] "S.a.l.i.m & Co.'s Café"                                                  
## [27] "Villa Vevrier"                                                           
## [28] "Big Weekend"                                                             
## [29] "The Racket Boys"                                                         
## [30] "The Soft Touch"                                                          
## [31] "Men's Egg Drummers"                                                      
## [32] "Frankenstein"                                                            
## [33] "Egression"                                                               
## [34] "She's Out of His Mind"                                                   
## [35] "Stan"                                                                    
## [36] "Faust Sonnengesang"                                                      
## [37] "Röhrls Katze"                                                            
## [38] "Much Ado About Nothing"                                                  
## [39] "Marija's Own"                                                            
## [40] "Bettada Jeeva"                                                           
## [41] "Deadmau5 Live @ Earls Court"                                             
## [42] "40-Life"                                                                 
## [43] "Payin' the Price"                                                        
## [44] "Acharya"                                                                 
## [45] "Nine Lives: A Musical Adaptation Live"                                   
## [46] "Tangled Up in Blue"                                                      
## [47] "South of Southern"                                                       
## [48] "Chocolate"                                                               
## [49] "Taken in"                                                                
## [50] "Erase una vez en Bolivia"
```

All we are changing is the date in the URL.

---

We cannot just keep copying and pasting our code for each year. It gets tiring!!!

Whenever you catch yourself copying and pasting code and only modifying a tiny part (e.g. year in the URL), write a function to automate the process. The tiny part that needs the modification can be the argument of the function.

---

---

---

---

```r
scrape_movie_title <- function(year) {
  page <- paste0("https://www.imdb.com/search/title/?title_type=feature&year=", year, "-01-01,", year, "-12-31&sort=user_rating,desc")
read_html(page) %>% 
  html_nodes(".lister-item-header a") %>% 
  html_text()
}
```

---

```r
scrape_movie_title(2002)
```

```
##  [1] "Venganza"                                            
##  [2] "Welcome to San Pedro"                                
##  [3] "The Cloud of Unknowing"                              
##  [4] "Americanos"                                          
##  [5] "Punarjani"                                           
##  [6] "Ayodhya Ramayya"                                     
##  [7] "JJ Cale in Session"                                  
##  [8] "Papsajt"                                             
##  [9] "Mage Wam Atha"                                       
## [10] "Check Mate"                                          
## [11] "Bakshis"                                             
## [12] "Destiny 101"                                         
## [13] "Engaging Peter"                                      
## [14] "A Mero Hajur"                                        
## [15] "Regarding Penelope's Wake"                           
## [16] "Montagna con Forza"                                  
## [17] "Book of Danny"                                       
## [18] "2 Fläschchen"                                        
## [19] "Dreaming in Black and White"                         
## [20] "Until Morning"                                       
## [21] "The Wishing Stone"                                   
## [22] "Only in Hollywood"                                   
## [23] "Living with the Fosters"                             
## [24] "Someone Is Sleeping in My Pain: An East-West Macbeth"
## [25] "Blackmailing Santa"                                  
## [26] "The Lord of the Rings: The Two Towers"               
## [27] "My Father's Daughter"                                
## [28] "Phulkumar"                                           
## [29] "West Bank Brooklyn"                                  
## [30] "My Brother's Light"                                  
## [31] "Matir Moina"                                         
## [32] "City of God"                                         
## [33] "Manmandir"                                           
## [34] "Khandan"                                             
## [35] "Simhadriya Simha"                                    
## [36] "Crackaparkz"                                         
## [37] "Appu"                                                
## [38] "Developing Sheldon"                                  
## [39] "Le Chant de la Noria"                                
## [40] "Who the Hell Is Bobby Roos?"                         
## [41] "Mutual Admiration Society"                           
## [42] "Filantropica"                                        
## [43] "Sexgunsmoney@20"                                     
## [44] "The Pianist"                                         
## [45] "Nomad"                                               
## [46] "Kanyadaan"                                           
## [47] "Yuva Ratna"                                          
## [48] "Peggy and Fred in Hell: The Complete Cycle"          
## [49] "Enki-Benki"                                          
## [50] "Yearbook"
```