get value from xml with r by attribute

Question

I'm trying to get values from xml that looks like this:

<data>
    <result name="r">
        <item>
            <str name="id">123</str>
            <str name="xxx">aaa</str>
        </item>
        <item>
            <str name="id">456</str>
            <str name="xxx">aaa</str>
        </item>
    </result>
</data>

So far, I can get the id value in the following way:

xmlfile <- xmlParse(url)
data <- xmlRoot(xmlfile) 
result <- xmltop[["result"]]
for (i in xmlSize(result)) {
  print(xmlValue(result[[i]][[1]]))
}

This seems highly inefficient and only works if "id" is stored in the first child element. So, is there a way to get the value of an element (123, 456) by searching for the attribute (name) and value (id)?

Answer 1

The xml2 package is very good for solving this type of problem.

library(xml2)
page<-read_xml('<data>
    <result name="r">
               <item>
               <str name="id">123</str>
               <str name="xxx">aaa</str>
               </item>
               <item>
               <str name="id">456</str>
               <str name="xxx">aaa</str>
               </item>
               </result>
               </data>')

#find all str nodes
 nodes<-xml_find_all(page, ".//str")
#filter out the nodes where the attribute name=id
 nodes<-nodes[xml_attr(nodes, "name")=="id"]
#get values (as character strings)
 xml_text(nodes)

Update

Using Xpath selectors everything can be accomplished in 1 line

#R verison >4.0
xml_find_all(page, ".//str[@name='id']") |> xml_text()

Here is a link to a handy xpath path cheat sheet: https://www.red-gate.com/simple-talk/development/dotnet-development/xpath-css-dom-and-selenium-the-rosetta-stone/