Find all parents as walking through a tree

Question

I want to use clojure.zip to walk through this tree and print the node and its parent. I am having trouble getting the parent. For example the parent of :e is :b.

;;
;;     :a
;;     / \
;;   :b  :c
;;   /\    \
;; :d :e   :f
;;
(def example [:a [:b [:d] [:e]] [:c [:f]]])
(def z (zip/vector-zip example))
(def locs (take-while (complement zip/end?) (iterate zip/next z)))

(defn parent-of [loc]
  (when-let [parent-loc (-> loc zip/up zip/left)]
    (zip/node parent-loc)))

(defn visit-all []
  (doseq [loc locs]
    (let [node (zip/node loc)]
      (when (keyword? node)
        (println node "has parent" (parent-of loc))))))

This is the result:

:a has parent nil
:b has parent :a
:d has parent :b
:e has parent [:d]
:c has parent [:b [:d] [:e]]
:f has parent :c

I could keep improving the parent-of function - my next thought would be to go to the left-most node. There will be an algorithm that will return the correct answer from all locations - however going about it this way seems like quite a lot of work for a common requirement.

Is there a better approach I should be taking?

Edit This question is not about clojure.walk or Spector. I am looking for an answer that uses clojure.zip and gives the parent as I defined it in the question, which is simply the keyword above the loc. So if the loc given to parent-of is :f I would expect it to return :c.

If someone can tell me, as a comment, that zippers are not really used anymore, and say clojure.walk or Spector is the current best practice way to go for navigating trees, then that would help.

Can you provide sample inputs and outputs for the function you are trying to implement? — OlegTheCat

amalloy amalloy · Accepted Answer · 2016-09-02T15:32:06

Why are you using zip/left? The parent of the node is exactly the node above it, not a node above it and to the left for some reason. Removing that is all you need to do.

Find all parents as walking through a tree

2 Answers