Duplicate a Sequence – Rich 4Clojure Problem 32 – See: https://github.com/PEZ/rich4clojure

rich4clojure_easy_problem_032.clj

(ns rich4clojure.easy.problem-032
  (:require [hyperfiddle.rcf :refer [tests]]))

;; = Duplicate a Sequence =
;; By 4Clojure user: dbyrne
;; Difficulty: Easy
;; Tags: [seqs]
;; 
;; Write a function which duplicates each element of a
;; sequence.

(def __ :tests-will-fail)

(comment
  
  )

(tests
  (__ [1 2 3]) := '(1 1 2 2 3 3)
  (__ [:a :a :b :b]) := '(:a :a :a :a :b :b :b :b)
  (__ [[1 2] [3 4]]) := '([1 2] [1 2] [3 4] [3 4])
  (__ [[1 2] [3 4]]) := '([1 2] [1 2] [3 4] [3 4]))

;; To participate, fork:
;; https://github.com/PEZ/rich4clojure

;; Post your solution below, please!

(def __ #(interleave % %))

(def __ (fn [l] (->> l (map (fn [x] [x x])) (apply concat))))

(defn dup
  [[frst & rst]]
  (when frst
    (lazy-seq (cons frst (cons frst (dup rst))))))

(def __ dup)

(def __ #(interleave % %))

(def __ (fn [cols] (mapcat #(list % %) cols)))

(def __ (fn [c] (mapcat (fn [a] [a a]) c)))
Really loving mapcat today