homeless.clj

(defn max-key*
  "Returns the x for which (k x) is greatest.
  Differs from `max-key` in that it uses `compare` instead of `>`."
  {:static true}
  ([k x] x)
  ([k x y] (if (pos? (compare (k x) (k y))) x y))
  ([k x y & more]
   (reduce #(max-key* k %1 %2) (max-key* k x y) more)))

(defn min-key*
  "Returns the x for which (k x) is least.
  Differs from `min-key` in that it uses `compare` instead of `<`."
  {:static true}
  ([k x] x)
  ([k x y] (if (neg? (compare (k x) (k y))) x y))
  ([k x y & more]
   (reduce #(min-key* k %1 %2) (min-key* k x y) more)))

(defn max-by [k coll & [default]]
  (if (seq coll)
    (apply max-key* k coll)
    default))

(defn min-by [k coll & [default]]
  (if (seq coll)
    (apply min-key* k coll)
    default))