How to remove all tags except for some using Nokogiri

问题

How do I remove all tags below a certain node except for some elements using Nokogiri? For example, using this setup:

src = <<EOS
<html>
  <body>
    <p>
      Hello <i>world</i>!
      This is <em>another</em> line.
      <p><h3>And a paragraph <em>with</em> a heading.</h3></p>
      <b>Third line.</b>
    </p>
  </body>
</html>
EOS

doc = Nokogiri::HTML(src)    
para = doc.at('//p')

How can I remove all elements in the paragraph (while preserving their content) except <i> and <b> elements? So the result would be:

<html>
  <body>
    <p>
      Hello <i>world</i>!
      This is another line.
      And a paragraph with a heading.
      <b>Third line.</b>
    </p>
  </body>
</html>

回答1:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="html" indent="yes"/>

    <xsl:template match="node() | @*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*"/>
        </xsl:copy>
    </xsl:template>

    <xsl:template match="em | p/p | h3">
        <xsl:apply-templates/>
    </xsl:template>
</xsl:stylesheet>

Applied to your sample, result will be:

<html>
    <body>
        <p>
      Hello 
            <i>world</i>!
      This is another line.
      And a paragraph with a heading.
            <b>Third line.</b>
        </p>
    </body>
</html>

EDIT as requested in comments.

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="html" indent="yes"/>

    <xsl:template match="node() | @*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*"/>
        </xsl:copy>
    </xsl:template>

    <xsl:template match="p//*[not(self::i or self::b)]">
        <xsl:apply-templates/>
    </xsl:template>
</xsl:stylesheet>

This will remove all elements (markup, not string-values) in p, except of i and b elements.

回答2:

Just to round out the examples, here's one using Nokogiri without XSLT:

require 'nokogiri'

src = <<EOS
<html>
  <body>
    <p>
      Hello <i>world</i>!
      This is <em>another</em> line.
      <p><h3>And a paragraph <em>with</em> a heading.</h3></p>
      <b>Third line.</b>
    </p>
  </body>
</html>
EOS

doc = Nokogiri::HTML(src)

if (doc.errors.any?)
  puts "doc.errors:"
  doc.errors.each do |e|
    puts "#{ e.line }: #{ e.to_s }"
  end
  puts
end

doc.search('//p/*').each do |n| 
  n.replace(n.content) unless (%w[i b].include?(n.name))
end

puts doc.to_html
# >> doc.errors:
# >> 6: Unexpected end tag : p
# >> 8: Unexpected end tag : p
# >> 
# >> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
# >> <html><body>
# >>     <p>
# >>       Hello <i>world</i>!
# >>       This is another line.
# >>       </p>
# >> <p></p>
# >> <h3>And a paragraph <em>with</em> a heading.</h3>
# >>       <b>Third line.</b>
# >>     
# >>   </body></html>

Notice that Nokogiri is not happy with the markup and did some fix-up. And, that the actual code to strip the tags was only three lines and could have been written on one.

回答3:

Flack gave the correct answer using an XSLT template, I provide a full Nokogiri based example here:

xslt = <<EOS
<stylesheet version="1.0" xmlns="http://www.w3.org/1999/XSL/Transform">
    <output method="html" indent="yes"/>

    <template match="node() | @*">
        <copy>
            <apply-templates select="node() | @*"/>
        </copy>
    </template>

    <template match="p//*[not(self::i or self::b)]">
        <apply-templates/>
    </template>
</stylesheet>
EOS

src = <<EOS
<html>
  <body>
    <p>
      Hello <i>world</i>!
      This is <em>another</em> line.
      <p><h3>And a paragraph <em>with</em> a heading.</h3></p>
      <b>Third line.</b>
    </p>
  </body>
</html>
EOS

doc       = Nokogiri::XML(src)
paragraph = doc.at('p')

xslt = Nokogiri::XSLT(xslt)
transformed_paragraph = xslt.transform(paragraph)
paragraph.replace transformed_paragraph.children

puts doc

Output:

<?xml version="1.0"?>
<html>
  <body>
    <p>
      Hello <i>world</i>!
      This is another line.
      And a paragraph with a heading.
      <b>Third line.</b>
    </p>
  </body>
</html>

来源：https://stackoverflow.com/questions/4885300/how-to-remove-all-tags-except-for-some-using-nokogiri

标签

ruby

xslt

nokogiri