R Web scraping from different URLs - r

Question

I am web scraping a page at
http://catalog.ihsn.org/index.php/catalog#_r=&collection=&country=&dtype=&from=1890&page=1&ps=100&sid=&sk=&sort_by=nation&sort_order=&to=2017&topic=&view=s&vk=
From this url, I have built up a dataframe through the following code:
dflist <- map(.x = 1:417, .f = function(x) {
Sys.sleep(5)
url <- ("http://catalog.ihsn.org/index.php/catalog#_r=&collection=&country=&dtype=&from=1890&page=1&ps=100&sid=&sk=&sort_by=nation&sort_order=&to=2017&topic=&view=s&vk=")
read_html(url) %>%
html_nodes(".title a") %>%
html_text() %>%
as.data.frame()
}) %>% do.call(rbind, .)
I have repeated the same code in order to get all the data I was interested in and it seems to work perfectly, although is of course a little slow due to the Sys.sleep() thing.
My issue has raised once I have tried to scrape the single projects descriptions that should be included in the dataframe.
For instance, the first project description is at
http://catalog.ihsn.org/index.php/catalog/7118/study-description
the second project description is at
http://catalog.ihsn.org/index.php/catalog/6606/study-description
and so forth.
My problem is that I can't find a dynamic way to scrape all the projects' pages and insert them in the data frame, being the number in the URLs not progressive nor at the end of the link.
To make things clearer, this is the structure of the website I am scraping:
1.http://catalog.ihsn.org/index.php/catalog#_r=&collection=&country=&dtype=&from=1890&page=1&ps=100&sid=&sk=&sort_by=nation&sort_order=&to=2017&topic=&view=s&vk=
1.1. http://catalog.ihsn.org/index.php/catalog/7118
1.1.a http://catalog.ihsn.org/index.php/catalog/7118/related_materials
1.1.b http://catalog.ihsn.org/index.php/catalog/7118/study-description
1.1.c. http://catalog.ihsn.org/index.php/catalog/7118/data_dictionary
I have scraped successfully level 1. but cannot level 1.1.b. (study-description) , the one I am interested in, since the dynamic element of the URL (in this case: 7118) is not consistent in the website's above 6000 pages of that level.

Answer 1

You have to extract the deeper urls from the .title a and then scrape those as well. Here's a small example on how to do that using rvest and the tidyverse
library(tidyverse)
library(rvest)
scraper <- function(x) {
Sys.sleep(5)
url <- sprintf("http://catalog.ihsn.org/index.php/catalog#_r=&collection=&country=&dtype=&from=1890&page=%s&ps=100&sid=&sk=&sort_by=nation&sort_order=&to=2017&topic=&view=s&vk=", x)
html <- read_html(url)
tibble(title = html_nodes(html, ".title a") %>% html_text(trim = TRUE),
project_url = html_nodes(html, ".title a") %>% html_attr("href"))
}
result <- map_df(1:2, scraper) %>%
mutate(study_description = map(project_url, ~read_html(sprintf("%s/study-description", .x)) %>% html_node(".xsl-block") %>% html_text()))
This isn't complete as to all the things you want to do, but should show you an approach.