R：将XML读取为data.frame

Question

I'm facing this issue, I could not read an .xml file to make it as a data.frame in R. I know that this question have already great answers here and here , but I'm not able to decline the answers to my necessity, so sorry if it's duplicate.

I have a .xml like this:

<?xml version='1.0' encoding='UTF-8'?>
<LexicalResource>
  <GlobalInformation label="Created with the standard propagation algorithm"/>
  <Lexicon languageCoding="UTF-8" label="sentiment" language="-">
    <LexicalEntry id="id_0" partOfSpeech="adj">
      <Lemma writtenForm="word"/>
      <Sense>
        <Confidence score="0.333333333333" method="automatic"/>
        <Sentiment polarity="negative"/>
        <Domain/>
      </Sense>
    </LexicalEntry>
        </Lexicon>
</LexicalResource>

Stored locally. So i tried this way:

library(XML)
    doc<-xmlParse("...\\test2.xml")
    xmldf <- xmlToDataFrame(nodes=getNodeSet(doc,"//LexicalEntry/Lemma/Sense/Confidence/Sentiment"))

but the result is this:

> xmldf
data frame with 0 columns and 0 rows

So I tried the xml2 package:

library(xml2)
pg <- read_xml("...test2.xml")

recs <- xml_find_all(pg, "LexicalEntry")

> recs
{xml_nodeset (0)}

I have a lack of knowledge in manipulating .xml files, so I think I'm missing the point. What am I doing wrong?

Answer 1

You need the attributes, not the values, that's why the methods you have used do not work, try something like this:

data.frame(as.list(xpathApply(doc, "//Lemma", fun = xmlAttrs)[[1]]), 
           as.list(xpathApply(doc, "//Confidence", fun = xmlAttrs)[[1]]), 
           as.list(xpathApply(doc, "//Sentiment", fun = xmlAttrs)[[1]]))

  writtenForm          score    method polarity
1        word 0.333333333333 automatic negative

Another option is to get all the attributes of the xml and build with them a data.frame:

df <- data.frame(as.list(unlist(xmlToList(doc, addAttributes = TRUE, simplify = TRUE))))
colnames(df) <- unlist(lapply(strsplit(colnames(df), "\\."), function(x) x[length(x)]))
df
                                            label writtenForm          score    method 
1 Created with the standard propagation algorithm        word 0.333333333333 automatic 
  polarity   id partOfSpeech languageCoding     label language
1 negative id_0          adj          UTF-8 sentiment        -