Idiomatic text munging in Clojure

Question

In getting accustomed to Clojure syntax, I wrote the following stutter function:

(defn doublelist [coll]
 (flatten (map (fn [x] [x x]) coll)))
(defn stutter [s]
 (clojure.string/join
 " " (doublelist (clojure.string/split s #" "))))

This duplicates every word in an input string:

(stutter "how are you?")
"how how are are you? you?"

The doublelist function bugs me. It seems that repeating items in a list should be possible without a call to flatten.

Any thoughts?

Answer 1

You may use mapcat to omit flatten:

user> (defn doublelist [coll]
 (mapcat #(repeat 2 %) coll))
#'user/doublelist
user> (doublelist [:a :b :c :d])
(:a :a :b :b :c :c :d :d)