z/filter

[shaunlebron]

Should we add z/filter to complement z/map?

(refer-clojure :exclude '[filter])
(require '[rewrite-clj.zip.removez :refer [remove-and-move-left]])

(defn filter [pred zloc]
  (z/subedit-node root
    #(if-let [last-child (-> % z/down z/rightmost)]
       (loop [loc last-child]
         (if (z/leftmost? loc)
           (cond-> loc (not (pred loc)) z/remove)
           (recur (if (pred loc)
                    (z/left loc)
                    (remove-and-move-left loc)))))
       %)))

(comment
  (->> (z/of-string "[[1 2] 3 [4 5]]")
       (filter (comp coll? z/sexpr))
       z/root-string
       ) ;; => [[1 2] [4 5]]
  (->> (z/of-string "[[1 2] 3 [4 5]]")
       (filter (comp not coll? z/sexpr))
       z/root-string
       ) ;; => [3]
  (->> (z/of-string "[1 2 3 4 5 6]")
       (filter (comp even? z/sexpr))
       z/root-string
       ) ;; => [2 4 6]
  (->> (z/of-string "[]")
       (filter (comp even? z/sexpr))
       z/root-string
       ) ;; => []
  )

[lread]

Hi @shaunlebron, nice to see you again!

Is this something you have added to your own toolkit and are finding essential?
Or are you just dabbling with ideas?

[shaunlebron]

Yeah I needed it for my project. It took me a long time to write so I wanted to save someone else the time.

[lread]

Thanks @shaunlebron, I'll take a deeper peek then!

[shaunlebron]

Thank you! And on second thought, maybe this can be done as a transducing process instead?

[lread]

I've been looking at your code. It seems pretty darn good as is to me.
(There is only one obvious typo, which probably happened during paste, root should be zloc)

There might (or might not) be some edge cases to work out, but those could be uncovered by unit tests.

Would you like to take a crack at a PR, or would you like me to take it from here?

[shaunlebron]

@lread thank you, would you mind taking it?

[lread]

Don't mind at all. I'll put it on my TODO list. When I get to it, I might have some follow-up questions/discussion for/with you.