How do you calculate the number of "levels" of descendants of a Nokogiri node?
You can call Nokogiri::XML::Node#ancestors.size
to see how deeply a node is nested. But is there a way to determine how deeply nested the most deeply nested child开发者_JS百科 of a node is?
Alternatively, how can you find all the leaf nodes that descend from a node?
The following code monkey-patches Nokogiri::XML::Node
for fun, but of course you can extract them as individual methods taking a node argument if you like. (Only the height
method is part of your question, but I thought the deepest_leaves
method might be interesting.)
require 'nokogiri'
class Nokogiri::XML::Node
def depth
ancestors.size
# The following is ~10x slower: xpath('count(ancestor::node())').to_i
end
def leaves
xpath('.//*[not(*)]').to_a
end
def height
tallest = leaves.map{ |leaf| leaf.depth }.max
tallest ? tallest - depth : 0
end
def deepest_leaves
by_height = leaves.group_by{ |leaf| leaf.depth }
by_height[ by_height.keys.max ]
end
end
doc = Nokogiri::XML "<root>
<a1>
<b1></b1>
<b2><c1><d1 /><d2><e1 /><e2 /></d2></c1><c2><d3><e3/></d3></c2></b2>
</a1>
<a2><b><c><d><e><f /></e></d></c></b></a2>
</root>"
a1 = doc.at_xpath('//a1')
p a1.height #=> 4
p a1.deepest_leaves.map(&:name) #=> ["e1", "e2", "e3"]
p a1.leaves.map(&:name) #=> ["b1", "d1", "e1", "e2", "e3"]
Edit: To answer just the question asked tersely, without wrapping it in re-usable pieces:
p a1.xpath('.//*[not(*)]').map{ |n| n.ancestors.size }.max - a1.ancestors.size
You can call Nokogiri::XML::Node#ancestors.size to see how deeply a node is nested. But is there a way to determine how deeply nested the most deeply nested child of a node is?
Use:
count(ancestor::node())
This expression expresses the number of ancesstors the context (current) node has in the document hierarchy.
To find the nesting level of the "most deeply nested child" one must first determine all "leaf" nodes:
descendant-or-self::node()[not(node())]
and for each of them get their nesting level using the above XPath expression.
Then the maximum nesting level has to be calculated (the maximum of all numbers produced ), and this last calculation is not possible with pure XPath 1.0.
This is possible to express in a single XPath 2.0 expression:
max(for $leaf in /descendant-or-self::node()[not(node())],
$depth in count($leaf/ancestor::node())
return
$depth
)
Update:
It is possible to shorten this XPath 2.0 expression even more:
max(/descendant-or-self::node()[not(node())]/count(ancestor::node()))
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