'externalptr' error in R using XML data


I am working with some XML data in R and running into errors regarding type 'externalptr'.

1) I get the following error when I try to use the xmlInternalTreeParse() function (part of XML package).

 doc = xmlInternalTreeParse(xmldatavariable)
    'Error in as.vector(x, "character") : cannot coerce type 'externalptr'
 to vector of type 'character''

2) I get this error when I try to write the XML data to a text file so I can look at it and see what the error might be.

write(xmldatavariable,"sample.txt")
Error in cat(list(...), file, sep, fill, labels, append) : 
      argument 1 (type 'externalptr') cannot be handled by 'cat'

Any suggestions? Thanks - Z


Answers:


The XML package works by making pointer document of the XML document your trying to manipulate.

The 'externalptr' are simply external pointers to the data within the xml document.

To access the data you need to use

Parsed.xml <- xmlTreeParse(xml) ## should be string with xml text
## get value of the first node
xmlValue(xml[[1]])
## get value of the third grandchild of the first node
xmlValue(xml[[1]][[45]][[3]])   

You need to access each node of the xml as a list.