我想通过对以前未分组的兄弟节点进行分组来转换 HTML 或 XML 文档。
例如，我想取如下片段：
<h2>Header</h2>
<p>First paragraph</p>
<p>Second paragraph</p>
<h2>Second header</h2>
<p>Third paragraph</p>
<p>Fourth paragraph</p>
进入这个：
<section>
<h2>Header</h2>
<p>First paragraph</p>
<p>Second paragraph</p>
</section>
<section>
<h2>Second header</h2>
<p>Third paragraph</p>
<p>Fourth paragraph</p>
</section>
这是否可以使用简单的 Xpath 选择器和像 Nokogiri 这样的 XML 解析器？还是我需要为此任务实现 SAX 解析器？
【问题讨论】：
这是一个通用解决方案，它根据标题级别及其以下同级创建<section> 元素的层次结构：
class Nokogiri::XML::Node
# Create a hierarchy on a document based on heading levels
# wrap : e.g. "<section>" or "<div class='section'>"
# stops : array of tag names that stop all sections; use nil for none
# levels : array of tag names that control nesting, in order
def auto_section(wrap='<section>', stops=%w[hr], levels=%w[h1 h2 h3 h4 h5 h6])
levels = Hash[ levels.zip(0...levels.length) ]
stops = stops && Hash[ stops.product([true]) ]
stack = []
children.each do |node|
unless level = levels[node.name]
level = stops && stops[node.name] && -1
end
stack.pop while (top=stack.last) && top[:level]>=level if level
stack.last[:section].add_child(node) if stack.last
if level && level >=0
section = Nokogiri::XML.fragment(wrap).children[0]
node.replace(section); section << node
stack << { :section=>section, :level=>level }
end
end
end
end
这是正在使用的代码，以及它给出的结果。
原始 HTML
<body>
<h1>Main Section 1</h1>
<p>Intro</p>
<h2>Subhead 1.1</h2>
<p>Meat</p><p>MOAR MEAT</p>
<h2>Subhead 1.2</h2>
<p>Meat</p>
<h3>Caveats</h3>
<p>FYI</p>
<h4>ProTip</h4>
<p>Get it done</p>
<h2>Subhead 1.3</h2>
<p>Meat</p>
<h1>Main Section 2</h1>
<h3>Jumpin' in it!</h3>
<p>Level skip!</p>
<h2>Subhead 2.1</h2>
<p>Back up...</p>
<h4>Dive! Dive!</h4>
<p>...and down</p>
<hr /><p id="footer">Copyright © All Done</p>
</body>
转换代码
# Use XML only so that we can pretty-print the results; HTML works fine, too
doc = Nokogiri::XML(html,&:noblanks) # stripping whitespace allows indentation
doc.at('body').auto_section # make the magic happen
puts doc.to_xhtml # show the result with indentation
结果
<body>
<section>
<h1>Main Section 1</h1>
<p>Intro</p>
<section>
<h2>Subhead 1.1</h2>
<p>Meat</p>
<p>MOAR MEAT</p>
</section>
<section>
<h2>Subhead 1.2</h2>
<p>Meat</p>
<section>
<h3>Caveats</h3>
<p>FYI</p>
<section>
<h4>ProTip</h4>
<p>Get it done</p>
</section>
</section>
</section>
<section>
<h2>Subhead 1.3</h2>
<p>Meat</p>
</section>
</section>
<section>
<h1>Main Section 2</h1>
<section>
<h3>Jumpin' in it!</h3>
<p>Level skip!</p>
</section>
<section>
<h2>Subhead 2.1</h2>
<p>Back up...</p>
<section>
<h4>Dive! Dive!</h4>
<p>...and down</p>
</section>
</section>
</section>
<hr />
<p id="footer">Copyright All Done</p>
</body>
这是一个不使用 XPath 而是使用 Nokogiri 的答案。我冒昧地使解决方案更加灵活，处理任意开始/停止（但不是嵌套部分）。
html = "<h2>Header</h2>
<p>First paragraph</p>
<p>Second paragraph</p>
<h2>Second header</h2>
<p>Third paragraph</p>
<p>Fourth paragraph</p>
<hr>
<p id='footer'>All done!</p>"
require 'nokogiri'
class Nokogiri::XML::Node
# Provide a block that returns:
# true - for nodes that should start a new section
# false - for nodes that should not start a new section
# :stop - for nodes that should stop any current section but not start a new one
def group_under(name="section")
group = nil
element_children.each do |child|
case yield(child)
when false, nil
group << child if group
when :stop
group = nil
else
group = document.create_element(name)
child.replace(group)
group << child
end
end
end
end
doc = Nokogiri::HTML(html)
doc.at('body').group_under do |node|
if node.name == 'hr'
:stop
else
%w[h1 h2 h3 h4 h5 h6].include?(node.name)
end
end
puts doc
#=> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
#=> <html><body>
#=> <section><h2>Header</h2>
#=> <p>First paragraph</p>
#=> <p>Second paragraph</p></section>
#=>
#=> <section><h2>Second header</h2>
#=> <p>Third paragraph</p>
#=> <p>Fourth paragraph</p></section>
#=>
#=> <hr>
#=> <p id="footer">All done!</p>
#=> </body></html>
对于 XPath，请参阅XPath : select all following siblings until another sibling
【讨论】：
section 标记中的通用代码。
使用 xpath 的一种方法是选择 h2 后面的所有 p 元素，并从中减去也跟随下一个 h2 的 p 元素：
doc = Nokogiri::HTML.fragment(html)
doc.css('h2').each do |h2|
nodeset = h2.xpath('./following-sibling::p')
next_h2 = h2.at('./following-sibling::h2')
nodeset -= next_h2.xpath('./following-sibling::p') if next_h2
section_tag = h2.add_previous_sibling Nokogiri::XML::Node.new('section',doc)
h2.parent = section_tag
nodeset.each {|n| n.parent = section_tag}
end
【讨论】：
XPath 只能从您的输入文档中选择内容，不能将其转换为新文档。为此，您需要 XSLT 或其他一些转换语言。我想如果你喜欢 Nokogiri，那么前面的答案会很有用，但为了完整起见，下面是 XSLT 2.0 中的样子：
<xsl:for-each-group select="*" group-starting-with="h2">
<section>
<xsl:copy-of select="current-group()"/>
</section>
</xsl:for-each-group>
【讨论】：