Hello, I am trying to access specific node from XML file in R.

See more:

R

Here is an example xml webpage I am accessing and parsing with XML package in R.
I am interested in accessing the following information.
<comment type="function"> and <comment type="subcellular location">,
Here is the code I am running but it extract the first comment node regardless of its attributes or type (function or subcellular location ). How can I specifically extract function and subcellular locatio. Further what if there are multiple function attributes in same XML file. How can I specify the number (order) in they appears.

What I have tried:

web <-"http://www.uniprot.org/uniprot/Q13651.xml"
html <- getURL(web, followlocation = TRUE)
doc = xmlInternalTreeParse(html,asText=T, useInternal = TRUE)
top = xmlRoot(doc, skip = F)
xmlSApply(top[[1]][["comment"]], xmlValue)

text 
"Receptor for IL10; binds IL10 with a high affinity."