in reply to directory listing to array tree

(ns tree-sample
  (:use [clojure.contrib str-utils map-utils]))

(def test-paths [
  "/usr/local/bin"
  "/var/www/data/stuff"
  "/var/www"
  "/var/www/data/misc"
  "/var/logs"
  "/var/logs/data"
  "/usr/fnord"
  ])

(defn split-path [p] (re-split #"/" p))

(defn path-to-map [p]
  (let [p-rev (reverse p)]
    (loop [hd (first p-rev) tl (rest p-rev) acc {}]
      (if (empty? tl)
        {hd acc}
        (recur (first tl) (rest tl) {hd acc})))))

(defn merge-trees [tl]
  (loop [hd (first tl) tl (rest tl) acc {}]
    (if (empty? tl)
      (deep-merge-with concat hd acc)
      (recur (first tl) (rest tl) (deep-merge-with concat hd acc)))))

(defn printTree 
  ([t] (printTree t 0))
  ([t indent]
    (let [prefix (apply str (repeat indent " "))
          dirs (sort (keys t))]
          (loop [curdir (first dirs) rd (rest dirs)]
            (println (if (zero? indent) "/" (str prefix "->")) curdir)
            (let [ch (get t curdir)]
              (when-not (empty? ch)
                (printTree ch (+ 2 indent))))
            (when-not (empty? rd)
              (recur (first rd) (rest rd)))))))

(println (str "test data:\n\t" (apply str (interpose "\n\t" test-paths
+))))

(println "tree:")
(printTree
  (merge-trees
    (map path-to-map
         (map split-path test-paths))))

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Update: Tweaked to sort directory names.

Update 2: And yes, I have the Perl version (which came out about ~4 lines shorter). No, it's left as an exercise for the reader. :)

The cake is a lie.
The cake is a lie.
The cake is a lie.

Replies are listed 'Best First'.
Re^2: directory listing to array tree
by ELISHEVA (Prior) on Sep 14, 2009 at 19:29 UTC
    Only 4 lines less?
    Read more... (1103 Bytes)

    By using the leading portions of the path as a hash key, the subscript separator variable, $; (see perlvar), you can preserve the exact ordering given by the OP. This also takes under 20 lines, excluding the strict and warnings declaration.

    Read more... (1087 Bytes)

    For the OP, I don't know that language is the real winner here in getting the volume of code down. Understanding the nature of the problem itself is far more important. PHP also has a split function and str-repeat takes the place of Perl's x operator, so this code could be translated virtually as is to PHP.

    Best, beth

    Update: ikegami is right, I'm not actually using $; but rather the path subsegments as the hash key. See strike out above for correction.

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      Your code doesn't use $; at all. Even if you didn't realize it, it seems you discovered that $; is useless here since you can't do $h{@segs}.

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      Yup, roughly four lines shorter reimplementing (virtually) the same approach (not counting shebangs, use strict-y pragmata, or blank lines). Not to mention things like I don't yet grok Clojure / FP well enough that I can do in it what my $t = \%tree; while( @parts ) { my $head = shift @parts; $t = ($t->{$head} ||= {}); } lets me do trivially in Perl, or a better way than (apply str (repeat indent " ") to do " " x $indent.

      The Perl version is certainly much "slimmer" than my Clojure (and less . . . "chatty"? "visually cluttered"?) at roughly half the number of characters: 

      $ wc *
      44     152    1258 tree.clj
      42     112     741 tree.plx
      86     264    1999 total

      [download]

      Also the OP had said they were trying to build a tree and traverse it; your above approach doesn't give a data structure that can be manipulated afterwards or walked multiple times (not that it's not shorter and yours preserves the original ordering (unlike mine), just that's what I read the OP as looking for).

      The cake is a lie.
      The cake is a lie.
      The cake is a lie.

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