Clojure. Update double nested value - clojure

Question

I'm kind of newbie with Clojure, all is new but pretty fun too. So I have this data:
{:test {:title "Some Title"}, :questions [
{:id 1, :full-question {:question "Foo question", :id 1, :answers [{:id 7, :question_id 1, :answer "Foobar answer"}, {:id 8, :question_id 1, :answer "Foobar answer two"}]}},
{:id 5, :full-question {:question "Foo question", :id 5, :answers [{:id 12, :question_id 5, :answer "Foobar answer"}]}},
{:id 9, :full-question {:question "Foo question", :id 9, :answers [{:id 14, :question_id 9, :answer "Foobar answer"}, {:id 20, :question_id 9, :answer "Foobar answer two"}]}}
]}
A "classic" Test->Question->Answer kind of data structure. And I have this new info:
(def new-answer {:id 33, :answer "Another foobar answer", :question-id 9 })
I need to update the first structure to add "new-answer" into the "answers" for the :id number 9 in the :questions vector.
I tried with the update-in function but I don't know what to tell the correspondent :id in the maps inside the two vectors. I mean, I don't know how to build the "path" where I want to make the change.

Answer 1

also, there is a nice library for that kind of structural editing, called specter
your case could be solved like this:
(require '[com.rpl.specter :refer [ALL AFTER-ELEM setval]])
(defn add-answer [data {question-id :question-id :as new-answer}]
(setval [:questions ALL #(== question-id (:id %)) :full-question :answers AFTER-ELEM]
new-answer data))
user> (add-answer data {:id 33, :answer "Another foobar answer", :question-id 9 })
;;=> {:test {:title "Some Title"},
;; :questions
;; [
;; ;; ... all other ids
;; {:id 9,
;; :full-question
;; {:question "Foo question",
;; :id 9,
;; :answers
;; [{:id 14, :question_id 9, :answer "Foobar answer"}
;; {:id 20, :question_id 9, :answer "Foobar answer two"}
;; {:id 33, :answer "Another foobar answer", :question-id 9}]}}]}

Answer 2

You have the right idea with update-in. You can first calculate the index in your questions vector, then create the path :questions, "question-index", :full-question, :answers. Then you may conj in your new answer:
(def data {...})
(defn index-by-id
[v id]
(first (filter #(= (:id (v %)) id) (range (count v)))))
(defn add-answer
[answer]
(let [q-index (index-by-id (:questions data) (:question-id answer))]
(update-in data [:questions q-index :full-question :answers]
conj answer)))

Answer 3

Using clojure, you have the update-in function found here and the assoc found here. You can use the code suggested by Alex for update-in. assoc is fairly similar,
(defn change [ma a-map id]
(assoc (:questions ma)
(if-let [xq (first (filter int? (map-indexed (fn [idx mp] (if (= (:id mp) id) idx nil)) (:questions ma))))]
xq
(inc (count ma)))
a-map))
You can update your map as
(change o-map n-map idx) ;;param-1 is map to change,
;;param-2 is new-answer,
;;idx is the :id to change.
You can also refer to assoc-in found here which also associates a value in a nested associative structure.
Hope this helps.