Example of creating maps from a list of items

mapsexample.clj

(ns mapsexample.core)

;; Version 1:
;; Given a list of items, loop through them, adding one at a time with `assoc`.

(defn build-map-1 [items]
  (loop [n      0           ;; index to loop through the items
         my-map (hash-map)] ;; or just {} for an empty hash-map
    (if (>= n (count items))
      my-map
      (let [key (nth items n)      ;; given an index, creates the key
            val (str "item " key)] ;; create a value 
        (recur (inc n)                     ;; increase n for the next iteration
               (assoc my-map key val)))))) ;; "update" my-map

;; (build-map-1 [3 4 5])
;; => {3 "item 3", 4 "item 4", 5 "item 5"}

;; Version 2:
;; Reducing small maps into a larger one

(defn key-value-for-item [item] ;; helper function, returns a small map for a given item
  (hash-map item (str "Item " item)))

;; (key-value-for-item 120)
;; => {120 "Item 120"}

(defn build-map-2 [items]
  (let [pairs (map key-value-for-item items)] ;; create pairs from the items
    (reduce merge (hash-map) pairs))) ;; roll everything into a larger map

;; (build-map-2 [20 30 40 50])
;; => {20 "Item 20", 30 "Item 30", 40 "Item 40", 50 "Item 50"}