Recursive Grouping

[Ari King]

The code below is supposed to group and nest values as key value pairs, while it does that it also encapsulates the pairs in lists; does anyone know why? See below for code and example (notice the embolden parentheses):

({"a" ({"dan" [["a" 2011 "dan"] ["a" 2010 "dan"]]})} {"b" ({"jon" [["b" 2011 "jon"]]})})

(defn nest [data criteria]
  (if (empty? criteria)
    data
    (for [[k v] (group-by #(nth % (-> criteria vals first)) data)]
      (hash-map k (nest v (rest criteria))))))

[Ari King]

Ari King wrote:The code below is supposed to group and nest values as key value pairs, while it does that it also encapsulates the pairs in lists; does anyone know why? See below for code and example (notice the embolden parentheses):

({"a" ({"dan" [["a" 2011 "dan"] ["a" 2010 "dan"]]})} {"b" ({"jon" [["b" 2011 "jon"]]})})

I figured it out, I had to add "into {} ...". From what I understand, I had to do this because "for" returns a lazy sequence hence the parentheses; thus I need to transform the sequence into a map.

(defn nest [data criteria]
  (if (empty? criteria)
    data
    (into (for [[k v] (group-by #(nth % (-> criteria vals first)) data)]
      (hash-map k (nest v (rest criteria)))))))