In Clojure how to apply function on a collection

Question

I am trying to apply function for extracting content of one tag from xml on a collection of tags. Basically, I am trying to make a function that will extract content from xml, like this

(defn get-events
[xz] 
 (map (juxt 
    #(zf/xml1-> % :title zf/text) 
    #(zf/xml1-> % :performers :performer :name zf/text) 
    #(zf/xml1-> % :start_time zf/text) 
     #(zf/xml1-> % :stop_time zf/text))
 (zf/xml-> xz  :events :event)))

And my solution so far looks like this

(ns datamodel

(:use 
[net.cgrand.enlive-html :as en-html ])
(:require
[clojure.zip :as z] 
[clojure.xml :as xml ]
[clojure.data.zip.xml :as zf]
 [clojure.java.io :as io]
))


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

(defn xz [url](z/xml-zip (xml/parse url)))

(defn xml-zipper [& tags](zf/xml-> (xz data-url) tags))

(defn func [& tags]#(zf/xml1-> (xml-zipper tags) % zf/text))

(def tags [:title :venue_name])

and in REPL when I try to apply func to tags like this

(map #((apply comp (reverse( func :events :event))) %) tags)

I get an empty collection ().

Answer 1

When defining tags you are not actually building a literal list but a call to :title with :venue_name as its argument. Try declaring tags as a list or a vector in the following way:

(def tags '(:title :venue_name)) ;list
(def tags [:title :venue_name]) ; vector

I suggest you clean up your code a little bit since there seems to be a number of problems with it:

1. Double requirement of clojure.data.zip.xml.
2. Extra parenthesis in the definition of the function xz.
3. xz is used as both an alias for a namespace and the name of a function.
4. Remove the enclosing parenthesis func anonymous function (#(zf/xml1-> (xml-zipper tags) % zf/text)), you are creating and calling that fn at the same time.

Hope it helps.

---

EDIT

I think I now get what you are trying to do. Here's a working version for the selector generator function: selector. Note that the argument tag can be either a single keyword or a sequence of keywords, in which case apply is used when calling xml1->.

(ns datamodel
  (:require [clojure.zip :as z] 
            [clojure.xml :as xml]
            [clojure.data.zip.xml :as zf]
            [clojure.java.io :as io]))

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

(defn parse [url]
  (z/xml-zip (xml/parse url)))

(defn selector [tag]
  (if (sequential? tag)
    #(apply zf/xml1-> % (concat tag [zf/text]))
    #(zf/xml1-> % tag zf/text)))

(defn get-events
  [xml & tags]
  (let [events (zf/xml-> xml :events :event)
        fs     (map selector tags)]
    (map (apply juxt fs) events)))

(-> data-url 
  parse 
  (get-events :title :start_time [:performers :performer :name] :stop_time)
  first 
  prn)