XML (version 3.1-1)

xmlTree: An internal, updatable DOM object for building XML trees

Description

This is a mutable object (implemented via a closure) for representing an XML tree, in the same spirit as xmlOutputBuffer and xmlOutputDOM but that uses the internal structures of libxml. This can be used to create a DOM that can be constructed in R and exported to another system such as XSLT (http://www.omegahat.org/Sxslt)

Usage

xmlTree(tag, attrs = NULL, dtd=NULL, namespaces=list(),
          doc = newXMLDoc(dtd, namespaces))

Value

• An object of class XMLInternalDOM that extends XMLOutputStream and has the same interface (i.e. ``methods'') as xmlOutputBuffer and xmlOutputDOM. Each object has methods for adding a new XML tag, closing a tag, adding an XML comment, and retrieving the contents of the tree.
• addTag
  create a new tag at the current position, optionally leaving it as the active open tag to which new nodes will be added as children
• closeTag
  close the currently active tag making its parent the active element into which new nodes will be added.
• addComment
  add an XML comment node as a child of the active node in the document.
• value
  retrieve an object representing the XML tree. See saveXML to serialize the contents of the tree.
• add
  degenerate method in this context.

Details

This creates a collection of functions that manipulate a shared state to build and maintain an XML tree in C-level code.

References

http://www.w3.org/XML, http://www.xmlsoft.org, http://www.omegahat.org

See Also

saveXML newXMLDoc newXMLNode xmlOutputBuffer xmlOutputDOM

Examples

z = xmlTree("people", namespaces = list(r = "http://www.r-project.org"))
z$setNamespace("r")

z$addNode("person", attrs = c(id = "123"), close = FALSE)
  z$addNode("firstname", "Duncan")
  z$addNode("surname", "Temple Lang")
  z$addNode("title", "Associate Professor")
  z$addNode("expertize", close = FALSE)
     z$addNode("topic", "Data Technologies")
     z$addNode("topic", "Programming Language Design")
     z$addNode("topic", "Parallel Computing")
     z$addNode("topic", "Data Visualization")
     z$addNode("topic", "Meta-Computing")
     z$addNode("topic", "Inter-system interfaces")
  z$closeTag()
  z$addNode("address", "4210 Mathematical Sciences Building, UC Davis")
z$closeTag()

  tr <- xmlTree("CDataTest")
  tr$addTag("top", close=FALSE)
  tr$addCData("x <- list(1, a='&');
x[[2]]")
  tr$addPI("S", "plot(1:10)")
  tr$closeTag()
  cat(saveXML(tr$value()))


  f = tempfile()
  saveXML(tr, f, encoding = "UTF-8")


  # Creating a node
x = rnorm(3)
z = xmlTree("r:data", namespaces = c(r = "http://www.r-project.org"))
z$addNode("numeric", attrs = c("r:length" = length(x)))


  # shows namespace prefix on an attribute, and different from the one on the node.
  z = xmlTree()
z$addNode("r:data",  namespace = c(r = "http://www.r-project.org", omg = "http://www.omegahat.org"), close = FALSE)
x = rnorm(3)
z$addNode("r:numeric", attrs = c("omg:length" = length(x)))


z = xmlTree("examples")
z$addNode("example", namespace = list(r = "http://www.r-project.org"), close = FALSE)
z$addNode("code", "mean(rnorm(100))", namespace = "r")


x = summary(rnorm(1000))
d = xmlTree()
d$addNode("table", close = FALSE)

d$addNode("tr", .children = sapply(names(x), function(x) d$addNode("th", x)))
d$addNode("tr", .children = sapply(x, function(x) d$addNode("td", format(x))))

d$closeNode()
cat(saveXML(d))

# Dealing with DTDs and system and public identifiers for DTDs.
# Just doctype
za = xmlTree("people", dtd = "people")
# no public element
zb = xmlTree("people", dtd = c("people", "", "http://www.omegahat.org/XML/types.dtd"))
# public and system
zc = xmlTree("people", dtd = c("people", "//a//b//c//d", "http://www.omegahat.org/XML/types.dtd"))