nested XML to data frame in R

Question

Hello I'm new to R and XML files.

I'm trying to get this XML SOAP response into a dataframe:

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <soap:Body>
    <PrepareDataByClientResponse xmlns="urn:HM-schema">
      <PrepareDataByClientResult>
        <READOUT>
          <SerialNumber>1728527</SerialNumber>
          <Date>1510505992000</Date>
          <Type>1</Type>
          <Value>78.2</Value>
          <Status>OK</Status>
        </READOUT>
        <READOUT>
          <SerialNumber>1728527</SerialNumber>
          <Date>1510509592000</Date>
          <Type>1</Type>
          <Value>76.87</Value>
          <Status>OK</Status>
        </READOUT>
        <READOUT>
          <SerialNumber>1728527</SerialNumber>
          <Date>1510513192000</Date>
          <Type>1</Type>
          <Value>75.61</Value>
          <Status>OK</Status>
        </READOUT>
        <READOUT>
          <SerialNumber>e2ddeed13b4cc4d132f8c6a67d67eed3</SerialNumber>
          <Date>4531528776000</Date>
          <Type>3</Type>
          <Value>230.68</Value>
          <Status>OK</Status>
        </READOUT>
      </PrepareDataByClientResult>
        </PrepareDataByClientResponse>
      </soap:Body>
    </soap:Envelope>

I have tried several options like:

xmlout <- do.call(rbind, xpathApply(xmldoc,'//soap:Envelope/soap:Body/PrepareDataByClientResponse', xmlToDataFrame))
xmlout <- as.data.frame(t(xpathSApply(xmldoc,"//readout",function(x) xmlSApply(x,xmlValue))))
xmlout <- as.data.frame(t(xmlSApply(xmldoc["/PrepareDataByClientResponse/PrepareDataByClientResult/READOUT"],xmlAttrs)),stringsAsFactors=FALSE)
xmlout <- ldply(xmlToList(xmldoc), data.frame)

After extensive research in SO and other google searches, I have been unable to produce the desired results. All I can get is a data frame with a single row and all the observations in a different column each.

I'm trying to get a table of READOUTS like:

    SerialNumber    Date            Type    Value    Status
1   1728527         1510505992000   1       78.2     OK
2   1728527         1510509592000   1       76.87    OK
3   1728527         1510513192000   1       75.61    OK

Is there any way to get this sort of table to work?

Thanks in advance.

Answer 1

Because you have a default namespace at the <PrepareDataByClientResponse> tag (ie, xmlns without a colon separated prefix), all its children follow under this default namespace.

To parse the <READOUT> tags, consider declaring a prefix to use in a getNodeSet() call. Below uses nm . Such a call can then be used inside the convenience method xmlToDataFrame which can easily migrate relatively flat XML like you have into dataframes:

library(XML)

doc <- xmlParse('/path/to/SOAP/Response.xml')

df <- xmlToDataFrame(doc, nodes=getNodeSet(doc, "//nm:READOUT",
                                           namespaces=c(nm="urn:HM-schema")))

df
#                       SerialNumber          Date Type  Value Status
# 1                          1728527 1510505992000    1   78.2     OK
# 2                          1728527 1510509592000    1  76.87     OK
# 3                          1728527 1510513192000    1  75.61     OK
# 4 e2ddeed13b4cc4d132f8c6a67d67eed3 4531528776000    3 230.68     OK