How to repeat string n times in idiomatic clojure way?

Question

In Ruby, "str" * 3 will give you "strstrstr". In Clojure, the closest I can think of is (map (fn [n] "str") (range 3)) Is there a more idiomatic way of doing it?

Solution 1

How about this?

(apply str (repeat 3 "str"))

Or just

(repeat 3 "str")

if you want a sequence instead of a string.

Solution 2

And one more fun alternative using protocols:

(defprotocol Multiply (* [this n]))

Next the String class is extended:

(extend String Multiply {:* (fn [this n] (apply str (repeat n this)))})

So you can now 'conveniently' use:

(* "foo" 3)

Solution 3

Just to throw some more awesome and hopefully thought-provoking solutions.

user=> (clojure.string/join (repeat 3 "str"))
"strstrstr"

user=> (format "%1$s%1$s%1$s" "str")
"strstrstr"

user=> (reduce str (take 3 (cycle ["str"])))
"strstrstr"

user=> (reduce str (repeat 3 "str"))
"strstrstr"

user=> (reduce #(.concat %1 %2) (repeat 3 "str"))
"strstrstr"

Solution 4

You could also use the repeat function from clojure.contrib.string. If you add this to your namespace using require such as

(ns myns.core (:require [clojure.contrib.string :as str]))

then

(str/repeat 3 "hello")

will give you

"hellohellohello"

Solution 5

Or use the repeat function that comes with clojure-contrib' string package. In that case you can use (clojure.contrib.string/repeat 3 "str") which results in "strstrstr".

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Comments

[Rinzler]

perfect! I knew there had to be something like repeat, just couldnt find it

[Joost Diepenmaat]

+1 for code that's an order of magnitude more perverted than clojure.contrib.string/repeat :)

[Eric Wilson]

This seems really useful, but it seems that it no longer exists. Do you know of a way to do this with Clojure 1.4?

[David J.]

Fun, but don't do this at home. :)

[Patrick]

@EricWilson clojure.contrib was mostly migrated to other places at the beginning of language version 1.3. clojure.contrib.string was migrated to clojure.string which does not appear to contain 'repeat' any longer.

[Andrea Richiardi]

I would also add then: (clojure.string/join (repeatedly 3 (partial str "str"))). Similar but different to the first one.

[Lassi]

Does apply hit a limit on the argument count if you have lots of repetitions?