count-vowels.clj

;; Try it in the REPL or eval in Light Table

(require '[clojure.string :as string])

(def vowels [:a :e :i :o :u])

(defn char-is-consonant?
  [char]
  (not-any? #{(keyword char)} vowels))

(def char-is-vowel? (complement char-is-consonant?))

(defn string-to-vec
  "Converts a string to a vector of strings"
  [string]
  (vec (drop 1 (string/split string #""))))

(defn count-vowels
  "Returns the number of vowels in a word"
  [word]
  (count (filter char-is-vowel? (string-to-vec word))))

(count-vowels "foobarbazbuzz")
;;-> 5

You can also use the regex engine:

(defn count-ascii-vowels [s]
  (count (re-seq #"(?i)[aeiou]" s)))

This will likely be the fastest for large inputs

Cool, I didn't realize that strings were directly filterable, and using a set for the filter is nice too. Thanks!