Subsequence replacement function
Is there a function that could replace subsequences? For example:
user> (good-fnc [1 2 3 4 5] [1 2] [3 4 5])
;; => [3 4 5 3 4 5]
I know there are for strings clojure.string/replace
:
user> (clojure.string/replace "fat cat caught a rat" "a" "AA")
;; => "fAAt cAAt cAAught AA rAAt"
Is there something similar for vectors and lists?
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3 answers
Here's a version that plays well with lazy inputs. Note that it can accept an infinite lazy sequence (range)
without an infinite loop, as the loop based version will.
(defn sq-replace
[match replacement sq]
(let [matching (count match)]
((fn replace-in-sequence [[elt & elts :as sq]]
(lazy-seq
(cond (empty? sq)
()
(= match (take matching sq))
(concat replacement (replace-in-sequence (drop matching sq)))
:default
(cons elt (replace-in-sequence elts)))))
sq)))
#'user/sq-replace
user> (take 10 (sq-replace [3 4 5] ["hello, world"] (range)))
(0 1 2 "hello, world" 6 7 8 9 10 11)
I allowed the sequence argument to be the last argument, as this is the Clojure convention for functions that execute sequence.
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My previous (now deleted) answer was wrong because it wasn't as trivial as I thought at first, here's my second attempt:
(defn seq-replace
[coll sub rep]
(letfn [(seq-replace' [coll]
(when-let [s (seq coll)]
(let [start (take (count sub) s)
end (drop (count sub) s)]
(if (= start sub)
(lazy-cat rep (seq-replace' end))
(cons (first s) (lazy-seq (seq-replace' (rest s))))))))]
(seq-replace' coll)))
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