Json Question posted in
Our archive of expertly curated questions and answers provides insights and solutions to common problems related to this popular data interchange format. From parsing and manipulating JSON data to integrating it with various programming languages and web services, our archive has got you covered. Start exploring today and take your JSON skills to the next level

Sort JSON/Map structure in clojure before serializing to string

I’m using json/write-str to serialize a nested JSON object to string.

Example data:

{ :c 1 :a { :d 0 :c 1 :e { :a 0 :1 4 }}}
; json/write-str
; output
{"c":1,"a":{"d":0,"c":1,"e":{"a":0,"1":4}}}

Expected output

{"a":{"c":1,"d":0,"e":{"1":4,"a":0}},"c":1}

This can be trivially solved in JavaScript with the second parameter into the JSON.stringify function, but there doesn’t seem to be an equivalent for Clojure.

Tags:

2

Answers


  1. 0

    The problem is that you have hash maps in your data and the order of elements is undefined there. You have to make sure all the maps in your data are sorted-map and the simplest way do so is to recursively replace all maps by sorted maps:

    
(require '[clojure.walk :refer [postwalk]])

(def sort-maps
  (partial postwalk (fn [x]
                      (if (map? x)
                        (into (sorted-map) x)
                        x))))

(def data {:c 1 :a {:d 0 :c 1 :e {:a 0 :1 4}}})

(sort-maps data)
;; result: {:a {:c 1, :d 0, :e {:1 4, :a 0}}, :c 1}

(json/generate-string (sort-maps data))
;; "{"a":{"c":1,"d":0,"e":{"1":4,"a":0}},"c":1}"
    Login or Signup to reply.
  2. 0

    in this exact case you could also use built in :value-fn option of that lib:

    user=> (defn smap [data] (if (map? data) (into (sorted-map) data) data))
#'user/smap

user=> (json/write-str (smap data) :value-fn #(smap %2))
"{"a":{"c":1,"d":0,"e":{"1":4,"a":0}},"c":1}"


user=> (json/write-str (smap {:x 10 :b {:c 20 :a {:9 100 :3 101}}}) :value-fn #(smap %2))
"{"b":{"a":{"3":101,"9":100},"c":20},"x":10}"

    but notice, that it only works on map values (e.g. it will not sort maps inside an array).

    so the walk solution from another answer is more versatile.

    there are more handy opts applicable in the docs

    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search