many-ways-to-the-count.clj

;How to count all occurrences of 42?
    (count (filter #{42} coll))
    
;How to express count using reduce?
    (defn my-count [coll] (reduce (fn [n _] (inc n)) 0 coll))
    
;How to count all occurrences of 42 using reduce?
    (reduce (fn [n _] (inc n)) 0 (filter #{42} coll))
    
;Can you get rid of the filter?
    (reduce (fn [n x] (if (= 42 x) (inc n) n)) 0 coll)
    
;I'd like the result to be {42 occurences-count}.
    (reduce (fn [m x] (if (= 42 x) (assoc m 42 (inc (m 42))) m)) {42 0} coll)
    
;42 is hardcoded in four places, it's bad!
    (reduce (fn [m x] (if (= 42 x) (assoc m x (inc (m x))) m)) {42 0} coll)