Community-powered documentation and examples for Clojure

;; combine it with map to apply a function

(def students
  [{:name "Alice" :age 23 :gender :female}
   {:name "Bob" :age 21 :gender :male}
   {:name "John" :age 23 :gender :male}
   {:name "Maria" :age 22 :gender :female}
   {:name "Julie" :age 22 :gender :female}])

(frequencies (map :gender students))
;; => {:female 3, :male 2}

(frequencies (map :age students))
;;=> {23 2, 21 1, 22 2}