Another extractor
In the previous exercise, we built a function that was able to extract the text content from H2 headers.
We'll try something else here: we want to extract all the links that exist on a specific page. To do this, we will need to call two httr functions: html_nodes(), with the css argument set to "a" (a is the HTML tag for links) and html_attr(), which extract a given attribute from a node — in our case, this attribute will be "href", which is the link address.
purrr and rvest has been loaded for you. You can still find the urls vector in your workspace.
Deze oefening maakt deel uit van de cursus
Intermediate Functional Programming with purrr
Oefeninstructies
Prefill the
html_nodes()with thecssargument set to"a".Create the
href()function, which will be a prefilled version ofhtml_attr().Compose a new combination of
href(),get_a()andread_html().Map this new function on the
urlsvector.
Praktische interactieve oefening
Probeer deze oefening eens door deze voorbeeldcode in te vullen.
# Create a partial version of html_nodes(), with the css param set to "a"
get_a <- ___(html_nodes, ___)
# Create href(), a partial version of html_attr()
href <- ___(___, name = "href")
# Combine href(), get_a(), and read_html()
get_links <- ___(___, ___, ___)
# Map get_links() to the urls list
res <- ___(urls, ___) %>%
set_names(urls)
# See the result
res