clojure.core/frequencies

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Type: function Added: Clojure 1.2 Examples: 3 Runnable: 2

([coll])

Returns a map from distinct items in coll to the number of times they appear.

Examples

by pkolloch on 2010-08-20 . May have evaluation errors. ▶

(frequencies ['a 'b 'a 'a]) {a 3, b 1}

by pharcosyle on 2017-04-13 ▶

;; Turn a frequency map back into a coll. (mapcat (fn [[x n]] (repeat n x)) {:a 2 :b 1 :c 3}) ;;=> (:a :a :b :c :c :c)

by bfontaine on 2021-04-09 ▶

;; 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}

Note by lispro06

(fn [coll]
   (let [gp (group-by identity coll)] 
      (zipmap (keys gp) (map #(count (second %)) gp))))

Note by danneu

(into {} (for [[k v] (group-by identity "abbbc")] [k (count v)]))

Note by ppsreejith

user=> (frequencies [3 6 2 6 8 7 'b 'c 3 5 3 4 7 6 'a])
{2 1, 3 3, 4 1, 5 1, 6 3, 7 2, 8 1, a 1, c 1, b 1}
user=> (frequencies [3 6 2 6 8 7 'b 'c])
{3 1, 6 2, 2 1, 8 1, 7 1, b 1, c 1}
;Note that the order of keys need not be in order of vector

Note by humorless

(defn frequencies-by
  "a generalized version of frequencies"
  [f coll]
  (let [gp (group-by f coll)]
    (zipmap (keys gp)  (map #(count (second %)) gp))))

See also

• clojure.core/group-by (7)
• clojure.core/distinct (3)

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