https://github.com/cran/XML
Tip revision: eb6c6e359b36cd19faaf4374f6db416b3ef1b259 authored by Duncan Temple Lang on 14 September 2006, 00:00:00 UTC
version 0.99-93
version 0.99-93
Tip revision: eb6c6e3
getNodeSet.Rd
\name{getNodeSet}
\alias{getNodeSet}
\title{Find matching nodes in an internal XML tree/DOM}
\description{
This function provides a way to find XML nodes that match a particular
criterion. It uses the XPath syntax and allows quite powerful
expressions for identifying nodes. The XPath language requires some
knowledge, but tutorials are available.
}
\usage{
getNodeSet(doc, path, namespaces = character())
}
\arguments{
\item{doc}{an object of class \code{XMLInternalDocument}}
\item{path}{a string (character vector of length 1) giving the
XPath expression to evaluate.}
\item{namespaces}{ a named character vector giving the
namespace prefix and URI pairs that are to be used
in the XPath expression and matching of nodes.
The prefix is just a simple string that acts as a short-hand
or alias for the URI that is the unique identifier for the
namespace.
The URI is the element in this vector and the prefix is the
corresponding element name.
One only needs to specify the namespaces in the XPath expression and
for the nodes of interest rather than requiring all the
namespaces for the entire document.
Also note that the prefix used in this vector is local only to the
path. It does not have to be the same as the prefix used in the
document to identify the namespace. However, the URI in this
argument must be identical to the target namespace URI in the
document. It is the namespace URIs that are matched (exactly)
to find correspondence. The prefixes are used only to refer to
that URI.
}
}
\details{
This calls the libxml routine \code{xmlXPathEval}.
}
\value{
The results can currently be different
based on the returned value from the XPath expression evaluation:
\item{list}{a node set}
\item{numeric}{a number}
\item{logical}{a boolean}
\item{character}{a string, i.e. a single character element.}
}
\references{\url{http://xmlsoft.org},
\url{http://www.w3.org/xml}
\url{http://www.w3.org/TR/xpath}
\url{http://www.omegahat.org/RSXML}
}
\author{Duncan Temple Lang <duncan@wald.ucdavis.edu>}
\note{
More of the XPath functionality provided by libxml can and may be
made available to the R package.
Facilities such as compiled XPath expressions, functions, ordered node
information,
Please send requests to the maintainer.
}
\seealso{
\code{\link{xmlTreeParse}} with \code{useInternalNodes} as \code{TRUE}.
}
\examples{
doc = xmlTreeParse(system.file("exampleData", "tagnames.xml", package = "XML"), useInternalNodes = TRUE)
getNodeSet(doc, "/doc//b[@status]")
getNodeSet(doc, "/doc//b[@status='foo']")
els = getNodeSet(doc, "/doc//a[@status]")
sapply(els, function(el) xmlGetAttr(el, "status"))
# Using a namespace
f = system.file("exampleData", "SOAPNamespaces.xml", package = "XML")
z = xmlTreeParse(f, useInternal = TRUE)
getNodeSet(z, "/a:Envelope/a:Body", c("a" = "http://schemas.xmlsoap.org/soap/envelope/"))
getNodeSet(z, "//a:Body", c("a" = "http://schemas.xmlsoap.org/soap/envelope/"))
# Get two items back with namespaces
f = system.file("exampleData", "gnumeric.xml", package = "XML")
z = xmlTreeParse(f, useInternal = TRUE)
getNodeSet(z, "//gmr:Item/gmr:name", c(gmr="http://www.gnome.org/gnumeric/v2"))
}
\keyword{file}
\keyword{IO}