Get content after header tag with Nokogiri - ruby

Question

I am playing with Nokogiri just to learn it and am trying to write a little CL scraper. Right now I am trying to match up each State on the main page with the cities underneath. Below is a snippet of the HTML:
<div class="colmask">
<div class="box box_1">
<h4>Alabama</h4>
<ul>
<li>auburn</li>
<li>birmingham</li>
<li>dothan</li>
<li>florence / muscle shoals</li>
<li>gadsden-anniston</li>
<li>huntsville / decatur</li>
<li>mobile</li>
<li>montgomery</li>
<li>tuscaloosa</li>
</ul>
<h4>Alaska</h4>
<ul>
<li>anchorage / mat-su</li>
<li>fairbanks</li>
<li>kenai peninsula</li>
<li>southeast alaska</li>
</ul>
I can already pull out just this div class of "colmask" easy enough. But now I am just trying to get the UL directly after each h4, but can't find a way to do it so far. Suggestions?

Answer 1

You can get ul elements after h4 using following-sibling:
require 'nokogiri'
html = <<-EOF
<div class="colmask">
<div class="box box_1">
<h4>Alabama</h4>
<ul>
<li>auburn</li>
<li>birmingham</li>
<li>dothan</li>
<li>florence / muscle shoals</li>
<li>gadsden-anniston</li>
<li>huntsville / decatur</li>
<li>mobile</li>
<li>montgomery</li>
<li>tuscaloosa</li>
</ul>
<h4>Alaska</h4>
<ul>
<li>anchorage / mat-su</li>
<li>fairbanks</li>
<li>kenai peninsula</li>
<li>southeast alaska</li>
</ul>
EOF
doc = Nokogiri::HTML(html)
doc.xpath('//h4/following-sibling::ul').each do |node|
puts node.to_html
end
To select ul after an h4 with exact text:
puts doc.xpath("//h4[text()='Alabama']/following-sibling::ul")[0].to_html

Answer 2

I'd do something like this:
require 'nokogiri'
doc = Nokogiri::HTML(<<EOT)
<h4>Alabama</h4>
<ul>
<li>auburn</li>
<li>birmingham</li>
</ul>
<h4>Alaska</h4>
<ul>
<li>anchorage / mat-su</li>
<li>fairbanks</li>
</ul>
EOT
states = doc.search('h4')
states_and_cities = states.map{ |state|
cities = state.next_element.search('li a')
[state.text, cities.map(&:text)]
}.to_h
At this point states_and_cities is a hash of arrays:
states_and_cities
# => {"Alabama"=>["auburn", "birmingham"],
# "Alaska"=>["anchorage / mat-su", "fairbanks"]}
If you're concerned about having a big structure, it'd be very easy to convert states to a hash where each state's name is a key, and the associated value is the state's node. Then, that node could be grabbed to find only the cities for the particular state.
However, if you're running this code to generate content for a web-page on the fly, then you're going about it wrong. The information for states and cities should be dumped into a database where it can be accessed much more quickly. Then you won't have to do it every time the page is generated.
Being kind and gentle to other sites is important; Research the HEAD HTTP request. It's your key to determining whether you should retrieve a page in full. Also, learn how to sniff the cache information from the HTTP header returned from a server. That tells you what your minimum refresh rate should be. Also, pay attention to the robots.txt file, which tells you what they consider safe for you to scrape; ignoring that can lead to being banned.