Getting a lazy list of the first n elements of a lazy list
In Clojure I have a list
[a, b, c, d]
and I want to pull a new infinite list of tuples out of it
[ [a,b,c], [b,c,d], [c,d,a], [d,a,b], [a,b,c] ... ]
I am trying to figure out how to do this in a purely functional way with the built-in seq functions.
Is this straight forward and I haven't cracked it yet? Or is it really some kind of difficult problem? (In other languages, I would write my own looping iterators and keep track of a lot of state.)
Update: Also, why would anyone vote for this?
+3
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2 answers
This can be accomplished with a combination of cycle and partition
(take 5 (partition 3 1 (cycle '(a b c d)))) ;; => ((a b c) (b c d) (c d a) (d a b) (a b c))
+10
Kyle
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Without using a section:
(defn next-rotation [coll]
(take (count coll) (drop 1 (cycle coll))))
(defn tuples [n coll]
(lazy-seq (cons (take n coll) (tuples n (next-rotation coll)))))
;; (take 5 (tuples 3 '(a b c d))) ;; =>
;; ((a b c) (b c d) (c d a) (d a b) (a b c))
+1
orend
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