R web scraping across multiple pages

Question

I am working on a web scraping program to search for specific wines and return a list of local wines of that variety. The problem I am having is multiple page results. The code below is a basic example of what I am working with

url2 <- "http://www.winemag.com/?s=washington+merlot&search_type=reviews"
htmlpage2 <- read_html(url2)
names2 <- html_nodes(htmlpage2, ".review-listing .title")
Wines2 <- html_text(names2)

For this specific search there are 39 pages of results. I know the url changes to http://www.winemag.com/?s=washington%20merlot&drink_type=wine&page=2, but is there an easy way to make the code loop through all the returned pages and compile the results from all 39 pages into a single list? I know I can manually do all the urls, but that seems like overkill.

Answer 1

You can do something similar with purrr::map_df() as well if you want all the info as a data.frame:

library(rvest)
library(purrr)

url_base <- "http://www.winemag.com/?s=washington merlot&drink_type=wine&page=%d"

map_df(1:39, function(i) {

  # simple but effective progress indicator
  cat(".")

  pg <- read_html(sprintf(url_base, i))

  data.frame(wine=html_text(html_nodes(pg, ".review-listing .title")),
             excerpt=html_text(html_nodes(pg, "div.excerpt")),
             rating=gsub(" Points", "", html_text(html_nodes(pg, "span.rating"))),
             appellation=html_text(html_nodes(pg, "span.appellation")),
             price=gsub("\\$", "", html_text(html_nodes(pg, "span.price"))),
             stringsAsFactors=FALSE)

}) -> wines

dplyr::glimpse(wines)
## Observations: 1,170
## Variables: 5
## $ wine        (chr) "Charles Smith 2012 Royal City Syrah (Columbia Valley (WA)...
## $ excerpt     (chr) "Green olive, green stem and fresh herb aromas are at the ...
## $ rating      (chr) "96", "95", "94", "93", "93", "93", "93", "93", "93", "93"...
## $ appellation (chr) "Columbia Valley", "Columbia Valley", "Columbia Valley", "...
## $ price       (chr) "140", "70", "70", "20", "70", "40", "135", "50", "60", "3...

Answer 2

You can lapply across a vector of the URLs, which you can make by pasting the base URL to a sequence:

library(rvest)

wines <- lapply(paste0('http://www.winemag.com/?s=washington%20merlot&drink_type=wine&page=', 1:39),
                function(url){
                    url %>% read_html() %>% 
                        html_nodes(".review-listing .title") %>% 
                        html_text()
                })

The result will be returned in a list with an element for each page.