[R] another XML package question

[Antje]

Hi Duncan,

thanks a lot for your explanations.

I tried the following now to understand a bit more:

data <- getNodeSet(doc, "//Data")
xmlName(data[[1]])
xmlName(xmlRoot(data[[1]]))
xpathApply(data[[1]], "./*", xmlName)

Is it right that using "data" in the xpathApply() somehow sets the current node 
but does not change the root?
So looking for a subnode at all levels below my current node is not possible 
with the xPath syntax? (search on all levels starting from root is possible 
with "//nodename")

Antje




Duncan Temple Lang schrieb:
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> Antje wrote:
>> Hi there,
>>
>> does anybody know how to return the xmlPath from a node?
>> For example, at several location in the xml file, I have nodes with the
>> same name and I'd like to process only the nodes from a certain path.
>>
>> Any idea?
> 
> As with your previous question, there are ways to do this
> with either XPath queries or R functions that operate on
> the nodes from the earlier queries.
> 
> By "xmlPath", let's assume you mean the ordered collection of
> nodes from the node to the root node of the document,
> i.e. the collection of ancestor nodes.
> So using XPath, you could use
> 
>    a = getNodeSet( node, "ancestor::*")
> 
> where node is the R variable containing the node within the tree
> whose ancestors you want, e.g.
>     getNodeSet(doc, "//val")[[1]]
> 
> The nodes in are in "reverse" order.
> 
> 
> You can do the same thing with the R function
> xmlParent().  To get the ancestors,
> 
>   tmp = xmlParent(node)
>   ans = list()
>   while( !is.null(tmp)) {
>       ans = c(ans, tmp)
>       tmp = xmlParent(tmp)
>   }
> 
> and of course in your case you could terminate the loop
> at any point.
> 
> 
> But a different approach to the problem is to use a more specific
> XPath query in the first place to get only the nodes of interest.
> For example, to get the <val> nodes in the second <data> node of
> your example, you could use
> 
>   getNodeSet(doc, "//data[2]/val")
> 
> or to find all <val> nodes which have the attribute  i = "t2",
> 
>    getNodeSet(doc, "//val[@i='t2']")
> 
> Or to find all <val> nodes with an ancestor which have an ancestor
> with an attribute name "loc"
> 
>      getNodeSet(doc, "//*[@loc='1']//val")
> 
> 
> 
> (
> The  sample XML document was
> 
> <root>
>    <data loc="1">
>      <val i="t1"> 22 </val>
>      <val i="t2"> 45 </val>
>    </data>
>    <data loc="2">
>      <val i="t1"> 44 </val>
>      <val i="t2"> 11 </val>
>    </data>
> </root>
> 
> )
> 
> 
>  D.
> 
>> Antje
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
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