R - Simple Recursive XML Parsing

This is intended for those who are starting out in R and interested in parsing an XML document recursively. It uses DT Lang's XML package.

If you want to just read certain types of nodes, then XPATH is great. This document by DT Lang is perfect for that.

However, if you want to read the whole document, then you have to recursively visit every node. Here's the way I ended up doing it. The generic function visitNode could be useful if you are just starting out reading XML in R.

	library(XML)
	#Recursive Function to visit the XML tree (depth first)
	visitNode <- function(node) {
	if (is.null(node)) {
	#leaf node reached. Turn back
	return()
	}
	print(paste("Node: ", xmlName(node)))
	num.children = xmlSize(node)
	if(num.children == 0 ) {
	# Add your code to process the leaf node here
	print( paste(" ", xmlValue(node)))
	}
	#Go one level deeper
	for (i in 1 : num.children) {
	visitNode(node[[i]]) #the i-th child of node
	}
	}
	xmlfile <- "books.xml"
	#read the XML tree into memory
	xtree <- xmlInternalTreeParse(xmlfile)
	root <- xmlRoot(xtree)
	visitNode(root)

view raw visitNode.R hosted with ❤ by GitHub

The full code, along with a sample XML file to test it is here.