Drop Every Nth Item – Rich 4Clojure Problem 41 – See: https://github.com/PEZ/rich4clojure

rich4clojure_easy_problem_041.clj

(ns rich4clojure.easy.problem-041
  (:require [hyperfiddle.rcf :refer [tests]]))

;; = Drop Every Nth Item =
;; By 4Clojure user: dbyrne
;; Difficulty: Easy
;; Tags: [seqs]
;; 
;; Write a function which drops every Nth item from a
;; sequence.

(def __ :tests-will-fail)

(comment
  
  )

(tests
  (__ [1 2 3 4 5 6 7 8] 3) := [1 2 4 5 7 8]
  (__ [:a :b :c :d :e :f] 2) := [:a :c :e]
  (__ [1 2 3 4 5 6] 4) := [1 2 3 5 6])

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

;; Post your solution below, please!

(def __ (fn [coll nth]
          (keep-indexed #(when (pos? (mod (inc %) nth)) %2) coll)))

(def __ #(->> %1 ( partition-all (- %2 1) %2) flatten))

(fn [seq1 nth-val]
(apply concat
(partition
(dec nth-val) ;parts size nth-val -1
nth-val ;size n step so each n is lost
(list) ; pad empty list to get leftovers of seq
seq1))))

(defn drop-at [coll idcs]
  (->> coll
       (map-indexed (fn [i n] [i n]))
       (remove (fn [[i x]] (some #{i} idcs)))
       (map second)))

(def __ (fn [xs n]
          (let [idcs (map dec (range 0 (inc (count xs)) n))]
            (drop-at xs (rest idcs)))))