Create a list from a string in Clojure

Question

I'm looking to create a list of characters using a string as my source. I did a bit of googling and came up with nothing so then I wrote a function that did what I wanted:

(defn list-from-string [char-string]
  (loop [source char-string result ()]
    (def result-char (string/take 1 source))
    (cond
     (empty? source) result
     :else (recur (string/drop 1 source) (conj result result-char)))))

But looking at this makes me feel like I must be missing a trick.

Is there a core or contrib function that does this for me? Surely I'm just being dumb right?
If not is there a way to improve this code?
Would the same thing work for numbers too?

TacticalCoder · Accepted Answer · 2012-05-11 18:31:49Z

55

You can just use seq function to do this:

user=> (seq "aaa")
(\a \a \a)

for numbers you can use "dumb" solution, something like:

user=> (map (fn [^Character c] (Character/digit c 10)) (str 12345))
(1 2 3 4 5)

P.S. strings in clojure are 'seq'able, so you can use them as source for any sequence processing functions - map, for, ...

edited May 11, 2012 at 18:31

TacticalCoder

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answered Jan 29, 2011 at 12:36

Alex Ott

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2 Comments

Polak Over a year ago

Hi! What is the meaning of [^Character c]? is ^Character to use Character/digit inside?

Alex Ott Over a year ago

this is type hint, without it the clojure will use reflection to determine the argument type. This makes the function slightly faster...

Matthew Boston · Accepted Answer · 2011-01-29 15:45:02Z

23

if you know the input will be letters, just use

user=> (seq "abc")
(\a \b \c)

for numbers, try this

user=> (map #(Character/getNumericValue %) "123")
(1 2 3)

edited Jan 29, 2011 at 15:45

answered Jan 29, 2011 at 14:04

Matthew Boston

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Comments

Markc · Accepted Answer · 2011-01-30 23:33:57Z

6

Edit: Oops, thought you wanted a list of different characters. For that, use the core function "frequencies".

clojure.core/frequencies
([coll])
  Returns a map from distinct items in coll to the number of times they appear.

Example:

user=> (frequencies "lazybrownfox")
{\a 1, \b 1, \f 1, \l 1, \n 1, \o 2, \r 1, \w 1, \x 1, \y 1, \z 1}

Then all you have to do is get the keys and turn them into a string (or not).

user=> (apply str (keys (frequencies "lazybrownfox")))
"abflnorwxyz"

edited Jan 30, 2011 at 23:33

answered Jan 30, 2011 at 23:27

Markc

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1 Comment

robertpostill Over a year ago

Thanks. I didn't want to get the frequencies but I was interested in the tip none-the-less.

murtaza52 · Accepted Answer · 2019-10-10 18:43:40Z

0

(apply str (set "lazybrownfox")) => "abflnorwxyz"

answered Oct 10, 2019 at 18:43

murtaza52

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