Clojurians Log v2

How would I go about selecting a specific node in a vector of vectors structure like the following:

[:html
 {}
 [:body
  {}
  [:table
   {}
   [:tr {} [:th {:colspan "1", :rowspan "1"} "Task Name"] [:th {:colspan "1", :rowspan "1"} "Description"]]
   [:tr
    {}
    [:td {:colspan "1", :rowspan "1"} [:a {:shape "rect", :href "Tasks/unpack.html"} "GUnzip/BUnzip2/UnXZ"]]
    [:td {:colspan "1", :rowspan "1"} [:p {} "Expands a file packed using GZip, BZip2 or XZ."]]]

don't need a complete answer, just need to understand which navigator to use in a case like this

somehow traverse to the first elems of vectors in the structure and if they match (in order) :html, :body, :table :tr then check a predicate against the first :td and collect string from the second :td if predicate matches

ok figured out a solution, a tad ugly but it works:

(defn tag? [name]
  (fn [vec]
    (and (vector? vec) (= (first vec) name))))

(spctr/select 
  [spctr/ALL (tag? :body) spctr/ALL (tag? :table) spctr/ALL (tag? :tr) ... etc]
  data)

@mbjarland you can capture more structure with this:

(defdynamicnav tags-traversal [& tags]
  (mapcat (fn [t] [ALL (tag? t)] tags))
  )

and then do (select [(tags-traversal :body :table :tr) ...] data)

@nathanmarz : ) for once I wasn't far off then! Thanks, that is indeed cleaner

@mbjarland btw, here's a better way to implement those:

(defn tag? [name]
  (pred
    (fn [vec]
      (and (vector? vec) (= (first vec) name)))))

(defdynamicnav tags-traversal [& tags]
  (let [late-tag? (late-resolved-fn tag?)]
    (mapcat (fn [t] [ALL (late-tag? t)]) tags)
    ))

adding pred to return of tag? increases performance by avoiding a runtime conversion from function to navigator

the late-resolved-fn call in tags-traversal allows that dynamicnav to handle dynamic parameters correctly (e.g. (tags-traversal :html some-local))

ok well that brings us back to the normal cycle of “no there’s a much better way to do that” : ) many thanks, will noodle on this

ok last one…how would I select the “rest” of a vector starting at an index…`srange` and srange-dynamic do not seem to do quite this from what I understand

@mbjarland do you know the index before the select happens?

yes

index is fixed

essentially it’s (rest (rest coll))

@mbjarland is this what you need?

(defn subrest [i]
  (srange-dynamic (fn [_] i) (fn [s] (count s))))

(transform (subrest 2) reverse [1 2 3 4 5 6])
;; => [1 2 6 5 4 3]