How to get child node of an XML page using Ruby and REXML

Question

I am using Ruby version 1.9.3. Here is a simple version of the actual XML page that I want to get information from. I need to access it from a secure website which requires login credentials. I can't use Nokogiri because I wasn't able to log into the website using it.

<root>
  <person>
    <name>Jack</name>
    <age>10</age>
  </person>
  <person>
    <name>Jones</name>
  </person>
  <person>
    <name>Jon</name>
    <age>16</age>
  </person>
</root>

As you can see sometimes the tag age does not appear. Using REXML with Ruby, I use the following code:

agent = Mechanize.new
xml = agent.get("https://securewebsite.com/page.xml")
document = REXML::Document.new(xml.body)

name = XPath.match(document, "//person/name").map {|x| x.text} 
# => ["Jack", "Jones", "Jon"]

age =  XPath.match(document, "//person/age").map {|x| x.text} 
# => ["10", "16"]

The problem is that I can't associate the age with the correct name because the index are now out of order. For example at index 1, name[1] is Jones but age[1] is 16. But that is not true because the person tag for Jones does not have the age tag.

Is there any way that I can get the age array to output: # => ["10", nil ,"16"] so that I can associate the correct name with its corresponding age?

Or is there a better way? Let me know if further explanation is required.

Answer 1

The problem is that we are looking at age and name as completely separate collections of information. What we need to do is get information from person as a collection.

xml = "<your xml here />"
doc = Nokogiri::XML(xml)
persons = doc.xpath("//person")
persons_data = persons.map {|person| 
  {
    name: person.xpath("./name").text,
    age: person.xpath("./age").text
  }
}

This gets the person nodes and then gets the related information from them giving a result:

puts persons_data.inspect #=> [
                                {:name=>"Jack", :age=>"10"}, 
                                {:name=>"Jones", :age=>""}, 
                                {:name=>"Jon", :age=>"16"}
                              ]

So to get the name and age of the first person you would call

persons_data[0]["name"] #=> "Jack"
persons_data[0]["age"]  #=> "10"

Answer 2

I'd do something like this:

require 'nokogiri'

doc = Nokogiri::XML(<<EOT)
<root>
  <person>
    <name>Jack</name>
    <age>10</age>
  </person>
  <person>
    <name>Jones</name>
  </person>
  <person>
    <name>Jon</name>
    <age>16</age>
  </person>
</root>
EOT

people = doc.search('person').each_with_object({}){ |person, h|
  age = person.at('age')
  h[person.at('name').text] = age ? age.text : nil
}

people # => {"Jack"=>"10", "Jones"=>nil, "Jon"=>"16"}

At that point, if I only want the ages, I'd use values:

people.values # => ["10", nil, "16"]

Retrieving a single person's age is trivial then:

people['Jon'] # => "16"
people['Jack'] # => "10"

---

I get this error when I'm using the .to_h method: ``block in ': undefined method to_h'

My mistake. to_h is not in older Rubies, but it's not needed because of how I'm generating the hash being returned. I adjusted the code above which will work in any Ruby that implements each_with_object.