Find Value of Specific Key in Nested Map

Question

In Clojure, how can I find the value of a key that may be deep in a nested map structure? For example:

(def m {:a {:b \"b\"
            :c \"c\"
            :d {         


        

Answer 1

Here is a version that will find the key without knowing the path to it. If there are multiple matching keys, only one will be returned:

(defn find-key [m k]
  (loop [m' m]
    (when (seq m')
      (if-let [v (get m' k)]
        v
        (recur (reduce merge
                       (map (fn [[_ v]]
                              (when (map? v) v))
                            m')))))))

If you require all values you can use:

(defn merge-map-vals [m]
  (reduce (partial merge-with vector)
          (map (fn [[_ v]]
                 (when (map? v) v))
               m)))

(defn find-key [m k]
  (flatten
   (nfirst
    (drop-while first
                (iterate (fn [[m' acc]]
                           (if (seq m')
                             (if-let [v (get m' k)]
                               [(merge-map-vals m') (conj acc v)]
                               [(merge-map-vals m') acc])
                             [nil acc]))
                         [m []])))))