R help - Apr 2011 - Treatment of xml-stylesheet processing instructions in XML module

Hello again,
Another stumble here that is defeating me.

I try:
a<-readLines(url("http://feeds.feedburner.com/grokin"))
t<-XML::xmlTreeParse(a, ignoreBlanks=TRUE, replaceEntities=FALSE,
asText=TRUE)
elem<- XML::getNodeSet(XML::xmlRoot(t),"/rss/channel/item")[[1]]

And I get:
Start tag expected, '<' not found
Error: 1: Start tag expected, '<' not found

When I modify the second line in "a" to remove the following (just
leaving the <rss> tag with its attributes), I do not get the error.
I removed:
<?xml-stylesheet type=\"text/xsl\" media=\"screen\"
href\"/~d/styles/rss2full.xsl\"?><?xml-stylesheet
type=\"text/css\" media\"screen\"
href=\"http://feeds.feedburner.com/~d/styles/itemcontent.css
\"?>

I would have expected the PI to be totally ignored by default.
Have I missed something??

Thanks in advance...

Cheers, Adam

Hi Adam

To use XPath and getNodeSet on an XML document,
you will want to use xmlParse() and not xmlTreeParse()
to parse the XML content. So

t = xmlParse(I(a)) # or asText = TRUE
elem = getNodeSet(t, "/rss/channel/item")[[1]]

works fine.

You don't need to specify the root node, but rather the document
in getNodeSet.

Also, if you have the package loaded, you don't need the XML::
prefix before the function  names.

  HTH
    D.

On 4/6/11 11:32 AM, Adam Cooper wrote:
> Hello again,
> Another stumble here that is defeating me.
> 
> I try:
> a<-readLines(url("http://feeds.feedburner.com/grokin"))
> t<-XML::xmlTreeParse(a, ignoreBlanks=TRUE, replaceEntities=FALSE,
> asText=TRUE)
> elem<-
XML::getNodeSet(XML::xmlRoot(t),"/rss/channel/item")[[1]]
> 
> And I get:
> Start tag expected, '<' not found
> Error: 1: Start tag expected, '<' not found
> 
> When I modify the second line in "a" to remove the following
(just
> leaving the <rss> tag with its attributes), I do not get the error.
> I removed:
> <?xml-stylesheet type=\"text/xsl\" media=\"screen\"
href> \"/~d/styles/rss2full.xsl\"?><?xml-stylesheet
type=\"text/css\" media> \"screen\"
href=\"http://feeds.feedburner.com/~d/styles/itemcontent.css
> \"?>
> 
> I would have expected the PI to be totally ignored by default.
> Have I missed something??
> 
> Thanks in advance...
> 
> Cheers, Adam
> 
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