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] "Hopeful Notes"                                                              
##  [2] "Lebensraum/Living Space"                                                    
##  [3] "Revolver: Poor Boyz"                                                        
##  [4] "Shakti Pirakkudhu"                                                          
##  [5] "Tebaatusasula"                                                              
##  [6] "Townbiz"                                                                    
##  [7] "Irdatlan Iroda"                                                             
##  [8] "Die Haushaltshilfe"                                                         
##  [9] "Dhinveynugehithaamaigaa"                                                    
## [10] "Min pinlige familie og mutantdræbersneglene"                                
## [11] "Dazed in Doon"                                                              
## [12] "DranDeh"                                                                    
## [13] "Truth & Life Dramatized Audio Bible"                                        
## [14] "Staying Gold"                                                               
## [15] "The Final Journey"                                                          
## [16] "It's Always Sunny in Philadelphia: Cast & Creators Live at the Paley Center"
## [17] "The Clock"                                                                  
## [18] "The Ballad of Frankie Silver"                                               
## [19] "Parastasul lui Viorel nu se mai tine aici"                                  
## [20] "Les Misérables in Concert: The 25th Anniversary"                            
## [21] "A3D Ayumi Hamasaki Arena Tour 2009 A: Next Level"                           
## [22] "Kisses, Chloe"                                                              
## [23] "Barriere"                                                                   
## [24] "Unbelehrbar"                                                                
## [25] "New Kids on the Block: Coming Home"                                         
## [26] "In Focus"                                                                   
## [27] "Inception"                                                                  
## [28] "Nobody Smiling"                                                             
## [29] "Heroes Crossing"                                                            
## [30] "Salvage Dream"                                                              
## [31] "The Beekeepers"                                                             
## [32] "The Art of Women"                                                           
## [33] "The Corners"                                                                
## [34] "The Toll"                                                                   
## [35] "Rat Rod Rockers!"                                                           
## [36] "Urban Wolf"                                                                 
## [37] "Grand Slammed"                                                              
## [38] "Jen"                                                                        
## [39] "Love Equation"                                                              
## [40] "Supériorité"                                                                
## [41] "Den relativt store DVD'en om Radioresepsjonen"                              
## [42] "The New Normal"                                                             
## [43] "Freedom Hills"                                                              
## [44] "Vecinos"                                                                    
## [45] "Sesame Street: C is for Cookie Monster"                                     
## [46] "Green Day: 21st Century Breakdown"                                          
## [47] "Life of the Party: Vol. II"                                                 
## [48] "National Theatre Live: Nation"                                              
## [49] "The Wizard of Agni"                                                         
## [50] "Slednecks 13"
```

---

## 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] "Deswa"                                                                   
##  [2] "Love on a Leash"                                                         
##  [3] "Rescue Team"                                                             
##  [4] "The Script: Homecoming"                                                  
##  [5] "Sans pudeur ni morale"                                                   
##  [6] "Tubero"                                                                  
##  [7] "Kill Bill: The Whole Bloody Affair"                                      
##  [8] "Watchtower"                                                              
##  [9] "Virtual Trek Wildlife Park"                                              
## [10] "The Nutcracker and the Mouse King"                                       
## [11] "Flashback"                                                               
## [12] "Myth & Mystery"                                                          
## [13] "American Actor"                                                          
## [14] "The Phantom of the Opera at the Royal Albert Hall"                       
## [15] "Stalemate"                                                               
## [16] "Mr. Plinkett's Indiana Jones and the Kingdom of the Crystal Skull Review"
## [17] "S.a.l.i.m & Co.'s Café"                                                  
## [18] "Gokuraku sentô: Kyonyû yumomi"                                           
## [19] "Big Weekend"                                                             
## [20] "Howling at the Moon"                                                     
## [21] "The Racket Boys"                                                         
## [22] "The Soft Touch"                                                          
## [23] "Men's Egg Drummers"                                                      
## [24] "Frankenstein"                                                            
## [25] "She's Out of His Mind"                                                   
## [26] "Stan"                                                                    
## [27] "Röhrls Katze"                                                            
## [28] "Much Ado About Nothing"                                                  
## [29] "40-Life"                                                                 
## [30] "Blood Eclipse"                                                           
## [31] "So Much Pain So in Love"                                                 
## [32] "Payin' the Price"                                                        
## [33] "Nine Lives: A Musical Adaptation Live"                                   
## [34] "Tangled Up in Blue"                                                      
## [35] "South of Southern"                                                       
## [36] "Taken in"                                                                
## [37] "Dark Blue"                                                               
## [38] "The Empty Hands"                                                         
## [39] "Translucent"                                                             
## [40] "Seksing Masahista"                                                       
## [41] "A-ha: Ending on a High Note - The Final Concert"                         
## [42] "Taza"                                                                    
## [43] "A Perfect Life"                                                          
## [44] "Half Empty"                                                              
## [45] "Bella Biondina"                                                          
## [46] "Where's My Stuff?"                                                       
## [47] "Bubbles"                                                                 
## [48] "Faust Sonnengesang"                                                      
## [49] "Billy Joel: Live at Shea Stadium"                                        
## [50] "The Hunting"
```

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] "A Mero Hajur"                                        
##  [2] "Welcome to San Pedro"                                
##  [3] "Americanos"                                          
##  [4] "Someone Is Sleeping in My Pain: An East-West Macbeth"
##  [5] "Papsajt"                                             
##  [6] "Check Mate"                                          
##  [7] "Bakshis"                                             
##  [8] "JJ Cale in Session"                                  
##  [9] "Destiny 101"                                         
## [10] "Engaging Peter"                                      
## [11] "Regarding Penelope's Wake"                           
## [12] "Montagna con Forza"                                  
## [13] "Book of Danny"                                       
## [14] "2 Fläschchen"                                        
## [15] "Maya Namara"                                         
## [16] "Until Morning"                                       
## [17] "Punarjani"                                           
## [18] "Only in Hollywood"                                   
## [19] "La gran sorpresa"                                    
## [20] "Blackmailing Santa"                                  
## [21] "The Lord of the Rings: The Two Towers"               
## [22] "My Father's Daughter"                                
## [23] "Peggy and Fred in Hell: The Complete Cycle"          
## [24] "West Bank Brooklyn"                                  
## [25] "The Cloud of Unknowing"                              
## [26] "My Brother's Light"                                  
## [27] "Matir moina"                                         
## [28] "City of God"                                         
## [29] "Manmandir"                                           
## [30] "Khandan"                                             
## [31] "Simhadriya Simha"                                    
## [32] "Mutual Admiration Society"                           
## [33] "Filantropica"                                        
## [34] "Sexgunsmoney@20"                                     
## [35] "The Pianist"                                         
## [36] "Nomad"                                               
## [37] "Babylonia en Guagua"                                 
## [38] "Enki-Benki"                                          
## [39] "Three"                                               
## [40] "Dogs Bark"                                           
## [41] "A Peck on the Cheek"                                 
## [42] "Urban Playground"                                    
## [43] "Motherly Love"                                       
## [44] "Mrtav 'ladan"                                        
## [45] "Wheatfield with Crows"                               
## [46] "Como perros de la calle"                             
## [47] "A Clean, Well-Lighted Place"                         
## [48] "Manmadhudu"                                          
## [49] "The Grail"                                           
## [50] "The Snowflake Crusade"
```