Decimal to Roman Numeral converter

destructuring1.clj

(let [lst (filter odd? [1 2 3 4 5])
      fst (first lst)
      snd (second lst)]
  (println fst snd))
=> 1 3

filter1.clj

(filter #(>= 6 (first %)) mapping)
=> ([5 "V"] [4 "IV"] [1 "I"])

(filter #(>= 4 (first %)) mapping)
=> ([4 "IV"] [1 "I"])

filter2.clj

(filter odd? [1 2 3 4 5])
=> (1 3 5)

fn1.clj

(fn [x]
  (>= i (first x)))

fn2.clj

#(>= i (first %))

mapping1.clj

{10 "X" 9 "IX" 5 "V" 4 "IV" 1 "I"}
=> {1 "I", 10 "X", 4 "IV", 5 "V", 9 "IX"}

mapping2.clj

(sorted-map 10 "X" 9 "IX" 5 "V" 4 "IV" 1 "I")
=> {1 "I", 4 "IV", 5 "V", 9 "IX", 10 "X"}

mapping3.clj

(sorted-map-by > 10 "X" 9 "IX" 5 "V" 4 "IV" 1 "I")
=> {10 "X", 9 "IX", 5 "V", 4 "IV", 1 "I"}

roman.clj

(def mapping (sorted-map-by > 1000 "M" 900 "CM" 500 "D" 400 "CD"
                            100 "C" 90 "XC" 50 "L" 40 "XL"
                            10 "X" 9 "IX" 5 "V" 4 "IV" 1 "I"))

(defn roman-numeral [i]
  (loop [i i s ""]
    (if (zero? i)
      s
      (let [[[n c]] (filter #(>= i (first %)) mapping)]
        (recur (- i n) (str s c))))))

seqmapping.clj

(seq (sorted-map-by > 10 "X" 9 "IX" 5 "V" 4 "IV" 1 "I"))
=> ([10 "X"] [9 "IX"] [5 "V"] [4 "IV"] [1 "I"])