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

xmlTree {XML} | R Documentation

## 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.net/Sxslt)

### Usage

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

### Arguments

`tag` | the node or element name to use to create the new top-level node in the tree or alternatively, an `XMLInternalNode` that was already created. This is optional. If it is not specified, no top-most node is created but can be added using `addNode`. If a top-level tag is added in the call to `xmlTree`, that becomes the currently active or open node (e.g. same as `addNode( ..., close = FALSE)`) and nodes subsequently added to this
`attrs` | attributes for the top-level node, in the form of a named character vector.
`dtd` | the name of the external DTD for this document. If specified, this adds the DOCTYPE node to the resulting document. This can be a node created earlier with a call to `newXMLDTDNode`, or alternatively it can be a character vector with 1, 2 or 3 elements giving the name of the top-level node, and the public identifier and the system identifier for the DTD in that order.
`namespaces` | a named character vector with each element giving the name space identifier and the corresponding URI, \ e.g `c(shelp = "http://www.omegahat.net/XML/SHelp")` If `tag` is specified as a character vector, these name spaces are defined within that new node.
`doc` | an internal XML document object, typically created with `newXMLDoc`. This is used as the host document for all the new nodes that will be created as part of this document. If one wants to create nodes without an internal document ancestor, one can alternatively specify this is as `NULL`.

### Details

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

### 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.

### Note

This is an early version of this function and I need to iron out some of the minor details.

### Author(s)

Duncan Temple Lang

### References

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

### 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='&');\nx[[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$addNode("r:data",  namespace = c(r = "http://www.r-project.org",
                                       omg = "http://www.omegahat.net"),
             close = FALSE)
    x = rnorm(3)
    z$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.net/XML/types.dtd"))
    # public and system
    zc = xmlTree("people",
                 dtd = c("people", "//a//b//c//d",
                         "http://www.omegahat.net/XML/types.dtd"))

[Package XML version 3.98-1.19 Index]