I'm pretty sure there has to be a more idiomatic way of writing this:
(defn update-2nd-level-vector
[map index value]
(assoc map :key1 (assoc (get map :key1) :key2 (-> map (get-in [:key1 :key2]) (assoc index value)))))
Example of its working:
=> (update-2nd-level-vector {:key1 {:key2 [0 1]}} 0 1)
{:key1 {:key2 [1 1]}}
you must use update-in..also your function is not enough flexible, you're restricted to use it only in maps with those keys..
this is a bit more practical
(defn update-level [keyspos mapp index value]
(assoc-in mapp keyspos (assoc (get-in mapp keyspos) index value)))
you can use it
(update-level [:key1 :key2] {:key1 {:key2 [0 1]}} 0 3)
or similar to your function
(def update-2nd-level-vector2 (partial update-level [:key1 :key2]))
(update-2nd-level-vector2 {:key1 {:key2 [0 1]}} 0 3)
update-in.