The Elegance of Clojure

elegance.clj

;; For a given list with N integers, return a new list removing the elements at odd positions.
;; Source: https://www.hackerrank.com/challenges/fp-filter-positions-in-a-list

;; My solution:
(fn[lst] 
    (map 
        #(when ((comp odd? first) %) 
            (println (second %)))
        (map-indexed list lst)))

;; A _much_ more elegant solution:
(fn [lst]
    (map second (partition 2 lst)))

It's worth pointing out that, for this particular problem, the elegant solution only works with an even number of elements in the original collection. With an odd number, and using partition with an n of 2, the last element of the original collection is dropped.

It's an easy enough fix:

(conj (vec lst) 0)

For example:

user=> (conj (vec '(1 2 3)) 0)
;; => [1 2 3 0]

This returns a new collection as a vector, but that's necessary, as conj'ing a new value to a list will place the new value at the beginning:

user=> (conj '(1 2 3) 0)
;; => (0 1 2 3)

The vector is treated the same as the list in the function in the gist.

Clojure does keep you on your toes :)

Just had a shower thought. Literally, came to me as I was shampooing my beard.

(fn [lst] 
    (rest (take-nth 2 (conj coll 0))))  



user=> (rest (take-nth 2 (conj '(8 15 22 1 10 6 2 18 18 1) 0)))
;; => (15 1 6 18 1)

I'll break it down later.