CODEWITHSUNDEEP
clojurexml-parsing
Vesna
Vesna

Reputation: 345

In CLojure how to call xml-> with arbitrary preds

I want to create a function that allows me to pull contents from some feed, here's what I have... zf is from here 

 (:require
        [clojure.zip :as z] 
        [clojure.data.zip.xml :only (attr text xml->)]
        [clojure.xml :as xml ]
        [clojure.contrib.zip-filter.xml :as zf]
        )

       (def data-url "http://api.eventful.com/rest/events/search?app_key=4H4Vff4PdrTGp3vV&keywords=music&location=Belgrade&date=Future")

     (defn zipp [data] (z/xml-zip data))

    (defn contents[cont & tags] 
      (assert (= (zf/xml-> (zipp(parsing cont)) (seq tags) text))))

but when I call it

(contents data-url :events :event :title)

I get an error java.lang.RuntimeException: java.lang.ClassCastException: clojure.lang.ArraySeq cannot be cast to clojure.lang.IFn (NO_SOURCE_FILE:0)

Upvotes: 1

Views: 582

Answers (1)

Michał Marczyk
Michał Marczyk

Reputation: 84341

(Updated in response to the comments: see end of answer for ready-made function parameterized by the tags to match.)

The following extracts the titles from the XML pointed at by the URL from the question text (tested at a Clojure 1.5.1 REPL with clojure.data.xml 0.0.7 and clojure.data.zip 0.1.1):

(require '[clojure.zip :as zip]
         '[clojure.data.xml :as xml]
         '[clojure.data.zip.xml :as xz]
         '[clojure.java.io :as io])

(def data-url "http://api.eventful.com/rest/events/search?app_key=4H4Vff4PdrTGp3vV&keywords=music&location=Belgrade&date=Future")
(def data (-> data-url io/reader xml/parse))
(def z (zip/xml-zip data))

(mapcat (comp :content zip/node)
        (xz/xml-> z
                  (xz/tag= :events)
                  (xz/tag= :event)
                  (xz/tag= :title)))

;; value of the above right now:
("Belgrade Early Music Festival, Gosta / Purcell: Dido & Aeneas"
 "Belgrade Early Music Festival, Gosta / Purcell: Dido & Aeneas"
 "Belgrade Early Music Festival, Gosta / Purcell: Dido & Aeneas"
 "VIII Early Music Festival, Belgrade 2013"
 "Kevlar Bikini"
 "U-Recken - Tree of Life Pre event"
 "Green Day"
 "Smallman - Vrane Kamene (Crows Of Stone)"
 "One Direction"
 "One Direction in Serbia")

Some comments:

  1. The clojure.contrib.* namespaces are all deprecated. xml-> now lives in clojure.data.zip.xml.

  2. xml-> accepts a zip loc and a bunch of "predicates"; in this context, however, the word "predicate" has an unusual meaning of a filtering function working on zip locs. See clojure.data.zip.xml source for several functions which return such predicates; for an example of use, see above.

  3. If you want to define a list of predicates separately, you can do that too, then use xml-> with apply:

    (def loc-preds [(xz/tag= :events) (xz/tag= :event) (xz/tag= :title)])
(mapcat (comp :content zip/node) (apply xz/xml-> z loc-preds))
;; value returned as above

Update: Here's a function which takes the url and keywords naming tags as arguments and returns the content found at the tags:

(defn get-content-from-tags [url & tags]
  (mapcat (comp :content zip/node)
          (apply xz/xml->
                 (-> url io/reader xml/parse zip/xml-zip)
                 (for [t tags]
                   (xz/tag= t)))))

Calling it like so:

(get-content-from-tags data-url :events :event :title)

gives the same result as the mapcat form above.

Upvotes: 4

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