XML to list and back to XML - r

Question

Situation: "Software" to R and back to "Software". The only interface for "Software" is xml.
In R, I need to make a few changes in the file so i convert it to a list and make some changes.
library(XML)
myFile = xmlParse("myXML")
xml_data <- xmlToList(myFile)
xml_data$timetable$train$.attrs[6] = "HelloNewWorld"
Now i need to convert this list "xml_data" it back to xml.
I found some functions like this:
function(item, tag) {
# just a textnode, or empty node with attributes
if(typeof(item) != 'list') {
if (length(item) > 1) {
xml <- xmlNode(tag)
for (name in names(item)) {
xmlAttrs(xml)[[name]] <- item[[name]]
}
return(xml)
} else {
return(xmlNode(tag, item))
}
}
# create the node
if (identical(names(item), c("text", ".attrs"))) {
# special case a node with text and attributes
xml <- xmlNode(tag, item[['text']])
} else {
# node with child nodes
xml <- xmlNode(tag)
for(i in 1:length(item)) {
if (names(item)[i] != ".attrs") {
xml <- append.xmlNode(xml, listToXml(item[[i]], names(item)[i]))
}
}
}
# add attributes to node
attrs <- item[['.attrs']]
for (name in names(attrs)) {
xmlAttrs(xml)[[name]] <- attrs[[name]]
}
return(xml)
}
But this doesnt work...
Any help or hints appreciated!
Thanks!
In the linked picture you can see the current xml-file. Highlighted in yellow the values that I need to change.
Link:
https://i.stack.imgur.com/remzj.png

Answer 1

Consider XSLT, the special-purpose language designed to transform XML files. No need to rewrite the entire tree in R. Using its xslt package (available on CRAN-R), extension of xml2, you can transform an input source and write output to screen or file.
Using the Identity Transform to copy document as is, below XSLT then rewrites one of the attributes in <train> tag, #source, similar to your above code attempt but with sixth attribute.
XML (sample input from railIML Wiki page)
<?xml version="1.0" encoding="UTF-8"?>
<railml xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance" xsi:noNamespaceSchemaLocation="timetable.xsd">
<timetable version="1.1">
<train trainID="RX 100.2" type="planned" source="opentrack">
<timetableentries>
<entry posID="ZU" departure="06:08:00" type="begin"/>
<entry posID="ZWI" departure="06:10:30" type="pass"/>
<entry posID="ZOER" arrival="06:16:00" departure="06:17:00" minStopTime="9" type="stop"/>
<entry posID="WS" departure="06:21:00" type="pass"/>
<entry posID="DUE" departure="06:23:00" type="pass"/>
<entry posID="SCW" departure="06:27:00" type="pass"/>
<entry posID="NAE" departure="06:29:00" type="pass"/>
<entry posID="UST" arrival="06:34:30" type="stop"/>
</timetableentries>
</train>
</timetable>
</railml>
XSLT (save as .xsl file, rewrites the #source attribute)
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="node()|#*">
<xsl:copy>
<xsl:apply-templates select="node()|#*"/>
</xsl:copy>
</xsl:template>
<xsl:template match="#source">
<xsl:attribute name="source">HelloNewWorld</xsl:attribute>
</xsl:template>
</xsl:stylesheet>
R
library(xslt)
doc <- read_xml("/path/to/Input.xml", package = "xslt")
style <- read_xml("/path/to/XLSTScript.xsl", package = "xslt")
new_xml <- xml_xslt(doc, style)
# OUTPUT TO SCREEN
cat(as.character(new_xml))
# OUTPUT TO FILE
write_xml(new_xml, "/path/to/Output.xml")
Output
<?xml version="1.0" encoding="UTF-8"?>
<railml xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance" xsi:noNamespaceSchemaLocation="timetable.xsd">
<timetable version="1.1">
<train trainID="RX 100.2" type="planned" source="HelloNewWorld">
<timetableentries>
<entry posID="ZU" departure="06:08:00" type="begin"/>
<entry posID="ZWI" departure="06:10:30" type="pass"/>
<entry posID="ZOER" arrival="06:16:00" departure="06:17:00" minStopTime="9" type="stop"/>
<entry posID="WS" departure="06:21:00" type="pass"/>
<entry posID="DUE" departure="06:23:00" type="pass"/>
<entry posID="SCW" departure="06:27:00" type="pass"/>
<entry posID="NAE" departure="06:29:00" type="pass"/>
<entry posID="UST" arrival="06:34:30" type="stop"/>
</timetableentries>
</train>
</timetable>
</railml>

Answer 2

I found it hard to apply many of the answers listed here so I wonder if this set of simple Java XML XPathHelper Unities may help others. You can find the source code here. I didn't write it all myself but adapted code I found, so I can't take all the credit but it works and it is compact and hope it helps others.
String xmlPayLoad = readFileAsString(payLoadPath + "/payLoad.xml");
TreeMap<String, String> header = new TreeMap<String, String>();
XPathHelperCommon xph = new XPathHelperCommon();
header = xph.findMultipleXMLItems(xmlPayLoad, "//header/*");
header.put("type", "newProcess");
xmlPayLoad = xph.modifyMultipleXMLItems(xmlPayLoad, "//header/*", header);
The primative XML header could be something like this:
<header>
<type>process</type>
<ruleBaseVersion>0</ruleBaseVersion>
<ruleBaseCommitment>0</ruleBaseCommitment>
<sequenceId>0</sequenceId>
<priortiseSID>0</priortiseSID>
<monitorIncomingEvents>0</monitorIncomingEvents>
<activityCount>0</activityCount>
<taskElapsedTime>0</taskElapsedTime>
<processStartTime>0</processStartTime>
<processElapsedTime>0</processElapsedTime>
<eventElapsedTime>0</eventElapsedTime>
<status>0</status>
</header>