network.clj

(comment
  user> (stabilize-by identity 3 [1 2 2 3 3 3 4 5 6 7])
  3
  user> (stabilize-by identity 3 [1 2 2 3 3 4 5 6 7])
  nil
  user> (stabilize-by #(* % %) 3 [1 -1 2 -2 2 3 3 4 5 6 7])
  2)

(defn stabilize-by [f n s]
  (when (seq s)
    (let [fs (map f s)
          [part rest] (split-with (comp #{(first fs)} f) s)]
      (if (= n (count (take n part)))
        (first part)
        (recur f n rest)))))

(defn stabilize-by [f n s]
  (->> s
    (partition-by f)
    (filter #(>= (count %) n))
    first first))