4Clojure - #32 Duplicate a Sequence

4Clojure - #32 Duplicate a Sequence

https://www.4clojure.com/problem/32

 

Write a function which duplicates each element of a sequence.

	(= (__ [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]))

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;; 32. Duplicate a Sequence

;; Write a function which duplicates each element of a sequence.

mapcat #(vector % %)

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mapcat #(list % %)

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### mapcat

user>  (mapcat #(list % %) [1 2 3])

(1 1 2 2 3 3)

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user> (doc mapcat)

clojure.core/mapcat

([f & colls])

  Returns the result of applying concat to the result of applying map

  to f and colls.  Thus function f should return a collection.

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user=> (source mapcat)

(defn mapcat

  "Returns the result of applying concat to the result of applying map

  to f and colls.  Thus function f should return a collection."

  {:added "1.0"}

  [f & colls]

    (apply concat (apply map f colls)))

nil

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user=> (map #(list % %) [1 2 3])

  ((1 1) (2 2) (3 3))

  user=> (concat (list '(1 1) '(2 2) '(3 3)))

  ((1 1) (2 2) (3 3))

  user=> (concat [1])

  (1)

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Solutions:

1

mapcat #(list % %)

maximental's solution:

1

mapcat #(list % %)

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hypirion's solution:

1

#(interleave % %)

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chouser's solution:

1

#(interleave % %)

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jafingerhut's solution:

1

(fn [s] (mapcat (fn [x] [x x]) s))

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