Filter element nodes in XML with Clojure zippers

Question

How can you filter text nodes in XML with Clojure zippers? For example, you may have a pretty-printed XML document that interleaves element nodes with text nodes containing whitespace:

(def doc
  "<?xml version=\"1.0\"?>
  <root>
    <a>1</a>
    <b>2</b>
  </root>")

If you want to retrieve the content of the root's children, you can do this:

(require '[clojure.data.xml :as xml]
         '[clojure.zip :as zip]
         '[clojure.data.zip :as zf]
         '[clojure.data.zip.xml :as zip-xml])

(-> doc
    xml/parse-str
    zip/xml-zip
    (zip-xml/xml-> :root zf/children zip-xml/text))

However, this returns (" " "1" " " "2" " "), including the whitespace.

How do you filter the zipper, so that only element nodes are selected?

I've come up with this.

(def filter-elements (comp (partial filter (comp xml/element? zip/node)) zf/children))

(-> doc
    xml/parse-str
    zip/xml-zip
    (zip-xml/xml-> :root filter-elements zip-xml/text))
; => ("1" "2")

I suspect it's unnecessarily complex and hence I'm looking for a better solution.

Answer 1

I think this relates to the general XML parsing problem of deciding which whitespace is meaningful and which isn’t. See for example this Q&A: Why am I getting extra text nodes as child nodes of root node?

I checked and found that data.xml does support skipping whitespace via an option :skip-whitespace. It’s undocumented though (source).

So best solve this at the parsing stage.

(-> doc
    (xml/parse-str :skip-whitespace true)
    zip/xml-zip
    (zip-xml/xml-> :root zf/children zip-xml/text))
; => ("1" "2")