[R] Need help extracting info from XML file using XML package

[Wacek Kusnierczyk]

Duncan Temple Lang wrote:
>
>> not really:  the xpath pattern '//coordinates' does say 'find all
>> coordinates nodes searching from the root', but the root here is not the
>> original root of the whole document, but each polygon node in turn.
>> try:
>>
>>     root = xmlInternalTreeParse('
>>         <root>
>>             <foo>
>>                 <bar>1</bar>
>>             </foo>
>>             <foo>
>>                 <bar>2</bar>
>>             </foo>
>>         </root>')
>>
>>     xpathApply(root, '//foo', xpathSApply, '//bar', xmlValue)
>>     # equals list("1", "2"), not list(c("1", "2"), c("1", "2"))
>>
>
> Just for the record and to avoid confusion for anyone reading the
> archives in the future,  the behaviour displayed above is from an old
> version of the XML package (mid 2008).   Subsequent versions yield
> the second result as  the //bar works from the root of the document.
> But using .//bar would search from the foo down the sub-tree.
>
> The reason for this is that, having used XPath to get a node, e.g.
> foo, we often want to go back up the XML tree from that current node,
> e.g.
>   ../
>   ./ancestor::foo
> and so on.

just for the record:  this is an excellent example of where the
behaviour (implementation + interface) of a package changes to make it
better, despite the trillions of lines of old code that get broken by
the change.  thanks, duncan.

vQ