13 Mode

(def numbers [1 2 2 3 3 3 4 4 4 4 5 5 5 5 5])

numbers

[1 2 2 3 3 3 4 4 4 4 5 5 5 5 5]

(frequencies numbers)

{1 1, 2 2, 3 3, 4 4, 5 5}

(sort-by second (frequencies numbers))

([1 1] [2 2] [3 3] [4 4] [5 5])

(last (sort-by second (frequencies numbers)))

[5 5]

(first (last (sort-by second (frequencies numbers))))

(defn mode [numbers]
  (first (last (sort-by second (frequencies numbers)))))

(mode numbers)

(mode [1 2 3 4 5 6])

Fixing the mode function

(defn mode [numbers]
  (let [freqs (frequencies numbers)
        max-freq (apply max (vals freqs))]
    (filter #(= (second %) max-freq) freqs)))

(mode numbers)

([5 5])

(mode [1 2 3 4 5 6])

([1 1] [2 1] [3 1] [4 1] [5 1] [6 1])

Extracting values from the mode function

(map first (mode numbers))

(5)

(map first (mode [1 2 3 4 5 6]))

(1 2 3 4 5 6)

(defn mode [numbers]
  (let [freqs (frequencies numbers)
        max-freq (apply max (vals freqs))]
    (map first (filter #(= (second %) max-freq) freqs))))

(mode numbers)

(5)

(mode [1 2 3 4 5 6])

(1 2 3 4 5 6)

(mode [1 1 2 2 3 3])

(1 2 3)

Return number if only single mode is present

(defn mode [numbers]
  (let [freqs (frequencies numbers)
        max-freq (apply max (vals freqs))]
    (if (= (count (filter #(= (second %) max-freq) freqs)) 1)
      (first (first (filter #(= (second %) max-freq) freqs)))
      (map first (filter #(= (second %) max-freq) freqs)))))

(mode [1 2 3 4 5 6])

(1 2 3 4 5 6)

(mode [3 1 1 2 2 3 3])

source: notebooks/mode.clj