https://github.com/cran/XML
Tip revision: c63073887a999d860870b00ba90b71bcd63b86ae authored by Duncan Temple Lang on 13 September 2011, 00:00:00 UTC
version 3.4-3
version 3.4-3
Tip revision: c630738
xmlGetAttr.Rd
\name{xmlGetAttr}
\alias{xmlGetAttr}
\title{Get the value of an attribute in an XML node}
\description{
This is a convenience function that retrieves
the value of a named attribute in an XML node,
taking care of checking for its existence.
It also allows the caller to provide a default
value to use as the return value if the
attribute is not present.
}
\usage{
xmlGetAttr(node, name, default = NULL, converter = NULL,
namespaceDefinition = character(),
addNamespace = length(grep(":", name)) > 0)
}
%- maybe also `usage' for other objects documented here.
\arguments{
\item{node}{the XML node}
\item{name}{the name of the attribute}
\item{default}{a value to use as the default return if the attribute
is not present in the XML node. }
\item{converter}{an optional function which if supplied is invoked
with the attribute value and the value returned.
This can be used to convert the string to an arbitrary
value which is useful if it is, for example, a number.
This is only called if the attribute exists within the node.
In other words, it is not applied to the \code{default} value.}
\item{namespaceDefinition}{a named character vector giving
name space prefixes and URIs to use when resolving for the
the attribute with a namespace.
The values are used to compare the name space prefix used in
the \code{name} given by the user to the name space
definition in the node to ensure they match.
This is important as we might ask for an attribute named
\code{r:width} assuming that the prefix \code{r} corresponded to the
URI \code{http://www.r-project.org}. However, there may
be a name space prefix \code{r} defined on the node that points
to a different URI and so this would be an erroneous match.
}
\item{addNamespace}{a logical value that indicates whether we should put the
namespace prefix on the resulting name.
This is passed on to \code{\link{xmlAttrs}} and so controls whether the resulting
attribute names have the prefix attached.
So one specifies \code{TRUE} for this argument if the attribute identifier
has a namespace prefix.
}
}
\details{
This just checks that the attribute list is
non-NULL and that there is an element with
the specified name.
}
\value{
If the
attribute is present,
the return value is a string which is the value of the attribute.
Otherwise, the value of \code{default} is returned.
}
\references{\url{http://www.w3.org/XML}, \url{http://www.jclark.com/xml},
\url{http://www.omegahat.org} }
\author{ Duncan Temple Lang }
\seealso{
\code{\link{xmlAttrs}}
}
\examples{
node <- xmlNode("foo", attrs=c(a="1", b="my name"))
xmlGetAttr(node, "a")
xmlGetAttr(node, "doesn't exist", "My own default value")
xmlGetAttr(node, "b", "Just in case")
}
\keyword{file}