| xml_find_all {xml2} | R Documentation |
Xpath is like regular expressions for trees - it's worth learning if
you're trying to extract nodes from arbitrary locations in a document.
Use xml_find_all to find all matches - if there's no match you'll
get an empty result. Use xml_find_one to find a specific match -
if there's no match you'll get an error.
xml_find_all(x, xpath, ns = character()) xml_find_one(x, xpath, ns = character())
x |
A document, node, or node set. |
xpath |
A string containing a xpath (1.0) expression. |
ns |
Optionally, a named vector giving prefix-url pairs, as produced
by |
xml_find_all always returns a nodeset: if there are no matches
the nodeset will be empty. The result will always be unique; repeated
nodes are automatically de-duplicated.
xml_find_one returns a node if applied to a node, and a nodeset
if applied to a nodeset. The output is always the same size as
the input. If there are no matches, xml_find_one will throw an
error; if there are multiple matches, it will use the first with a warning.
x <- read_xml("<foo><bar><baz/></bar><baz/></foo>")
xml_find_all(x, ".//baz")
xml_path(xml_find_all(x, ".//baz"))
# Note the difference between .// and //
# // finds anywhere in the document (ignoring the current node)
# .// finds anywhere beneath the current node
(bar <- xml_find_all(x, ".//bar"))
xml_find_all(bar, ".//baz")
xml_find_all(bar, "//baz")
# Find all vs find one -----------------------------------------------------
x <- read_xml("<body>
<p>Some <b>text</b>.</p>
<p>Some <b>other</b> <b>text</b>.</p>
</body>")
para <- xml_find_all(x, ".//p")
# If you apply xml_find_all to a nodeset, it finds all matches,
# de-duplicates them, and returns as a single list. This means you
# never know how many results you'll get
xml_find_all(para, ".//b")
# xml_find_one only returns one match per input node. If there are 0
# matches it will throw an error; if there are more than one it picks
# the first with a warning
xml_find_one(para, ".//b")
# Namespaces ---------------------------------------------------------------
# If the document uses namespaces, you'll need use xml_ns to form
# a unique mapping between full namespace url and a short prefix
x <- read_xml('
<root xmlns:f = "http://foo.com" xmlns:g = "http://bar.com">
<f:doc><g:baz /></f:doc>
<f:doc><g:baz /></f:doc>
</root>
')
xml_find_all(x, ".//f:doc")
xml_find_all(x, ".//f:doc", xml_ns(x))