Object not found in R language - r

Question

I am newbie at using R and here's my attempt to play a round a code to scrape quotes from multiple pages
# Load Libraries
library(rvest) # To Scrape
library(tidyverse) # To Manipulate Data
# Scrape Multiple Pages
for (i in 1:4){
site_to_scrape <- read_html(paste0("http://quotes.toscrape.com/page/",i))
temp <- site_to_scrape html_nodes(".text") html_text()
content <- append(content, temp)
}
#Export Results To CSV File
write.csv(content, file = "content.csv", row.names = FALSE)
I have encountered an error Object not found as for content variable. How can I overcome this error and set the object so as to be reusable in the append line?

Answer 1

Growing vector in a loop is very inefficient if you are scraping many pages. Instead what you should do is initialise a list with specific length which you know beforehand.
library(rvest)
n <- 4
content = vector('list', n)
# Scrape Multiple Pages
for (i in 1:n){
site_to_scrape <- read_html(paste0("http://quotes.toscrape.com/page/",i))
content[[i]] <- site_to_scrape %>%
html_nodes(".text") %>%
html_text()
}
write.csv(unlist(content), file = "content.csv", row.names = FALSE)
Another option without initialising is to use sapply/lapply :
all_urls <- paste0("http://quotes.toscrape.com/page/",1:4)
content <- unlist(lapply(all_urls, function(x)
x %>% read_html %>% html_nodes(".text") %>% html_text()))

Answer 2

I have searched and found the way to assign empty object before the loop content = c()
# Load Libraries
library(rvest) # To Scrape
library(tidyverse) # To Manipulate Data
content = c()
# Scrape Multiple Pages
for (i in 1:4){
site_to_scrape <- read_html(paste0("http://quotes.toscrape.com/page/",i))
temp <- site_to_scrape %>%
html_nodes(".text") %>%
html_text()
content <- append(content, temp)
}
#Export Results To CSV File
write.csv(content, file = "content.csv", row.names = FALSE)