XPath for numeric latitude and longitude values in R?

Question

I have an XML file with measurements. I would like to select only those measurementSiteName's that have a latitude and longitude using R.

With this code chunk I can select the name of a site with a specific latitude:

doc <- xml2::read_xml('test.xml')
query <- ".//measurementSiteName/values/value[../../../measurementSiteLocation/locationForDisplay/latitude/text() = '52.23634']"
xml2::xml_text(xml2::xml_find_all(doc, query))

However, there are site names without a latitude or longitude. I don't know how to do this. The latitude and longitude nodes may be missing or empty.

Can somebody please help me out? Please find attached text.xml

<measurements>
  <measurement>
    <measurementSiteName>
      <values>
          <value>abc</value>
      </values>
    </measurementSiteName>
    <measurementSiteLocation>
      <locationForDisplay>
        <latitude>52.23634</latitude>
        <longitude>4.503404</longitude>
      </locationForDisplay>
    </measurementSiteLocation>
  </measurement>
  <measurement>
    <measurementSiteName>
      <values>
          <value>def</value>
      </values>
    </measurementSiteName>
    <measurementSiteLocation>
      <locationForDisplay>
        <latitude></latitude>
        <longitude></longitude>
      </locationForDisplay>
    </measurementSiteLocation>
  </measurement>
  <measurement>
    <measurementSiteName>
      <values>
          <value>ghi</value>
      </values>
    </measurementSiteName>
    <measurementSiteLocation>
      <locationForDisplay>
      </locationForDisplay>
    </measurementSiteLocation>
  </measurement>
</measurements>

kjhughes · Accepted Answer · 2020-11-12 13:55:35Z

1

This XPath,

//measurementSiteLocation
  [locationForDisplay[    number(latitude)  = number(latitude) 
                      and number(longitude) = number(longitude)]]

will select all measurementSiteLocation elements with a locationForDisplay child that has latitude and longitude children with numeric values.

References:

Numeric predicate technique: See Dimitre's answer to XPath test if node value is number

answered Nov 12, 2020 at 13:55

kjhughes

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