I'm trying to iterate over a list with a given step in clojure.
In python I would have done the following :
xs = list(range(10))
xs[::2]
# out: [0, 2, 4, 6, 8]
xs[1::2]
# out: [1, 3, 5, 7, 9]
I can't figure out a clojure solution that feels idiomatic.
Here is the best I can think of:
(defn iterate-step-2 [xs]
(map first (take-while some? (iterate nnext xs))))
(iterate-step-2 (range 10))
; out: (0 2 4 6 8)
(iterate-step-2 (rest (range 10)))
; out: (1 3 5 7 9)
But it's not as generic (step is not configurable) and as flexible as the python solution. Plus it seems overly complicated.
Is there a better way to do this ?
;; equivalent to Python's your_seq[1:7:2] would be:
(->> your-seq (drop 1) (take 7) (take-nth 2))
;; equivalent to Python's your_seq[::2] would be:
(->> your-seq (take-nth 2))
;; equivalent to Python's your_seq[2:4:-3] would be:
(->> your-seq (take 4) (drop 2) (reverse) (take-nth 3))
;; equivalent to Python's your_seq[2:-4:-1]:
(->> your-seq (take (+ 1 (- (length your-seq) 4))) (drop 2) (reverse))
thank you for the detailed example, that's very helpful.
welcome! One has to
take
first an thendrop
I realized. Corrected.Just be careful, the last two examples which use the length and reverse on the seq will struggle on infinite sequences.