xml_find_num: should handle missing node;

[discoleo]

Example:
xml_find_num(xml, "/some/path/that/does/not/exist")

Should check if it is a request for NUMBER:
if (result_ == NULL) {
// should first check if the request is for NUMBER and return a NA;
SEXP ret = PROTECT(Rf_allocVector(VECSXP, 0));
Rf_setAttrib(ret, R_ClassSymbol, Rf_mkString("xml_missing"));
UNPROTECT(1);
return ret;
}

For missing nodes:

• either return NA;
• or add argument to function: xml_find_num(xml, xpath, defaultVal=NA);

[hadley]

Can you please provide a minimal reprex (reproducible example)? The goal of a reprex is to make it as easy as possible for me to recreate your problem so that I can fix it: please help me help you! If you've never heard of a reprex before, start by reading about the reprex package, including the advice further down the page. Please make sure your reprex is created with the reprex package as it gives nicely formatted output and avoids a number of common pitfalls.

[hadley]

I've closed this issue due to lack of requested reprex. If you still care about this bug, please open a new issue with a reprex.

[discoleo]

Unfortunately, I do not remember the details anymore. It may have been something like this - but i will have to check:

1. Search a nodeset using an initial XPATH, e.g. a set of PubMed articles in a larger xml matching some search criteria;
2. extract the year of publication as a numeric value, using another XPATH (which has some additional tokens in the path);

Some articles may lack the Year-field. I think that the vapply will generate an error. I will need to check when I have some time.