Sample code from Pune Clojure Dojo Meetup session held at 8 feb 2013.

freq.clj

(ns ^{:doc "Word frequencies in a text file."
      :author "Baishampayan Ghose <b.ghose@helpshift.com>"}
  meetup.freq
  (:require [clojure.java.io :as io]
            [clojure.string :as s]))

(def stop-word? #{"is" "the" "am" "i" "that" "if"}) ;; fill it up!

;;; all these functions are written in a "point free" style
(def get-lines (comp line-seq io/reader))

(def get-words (partial mapcat (partial re-seq #"\w+")))

(def lowercase-words (partial map s/lower-case))

(def remove-stop-words (partial remove stop-word?))

(defn count-freqs
  [coll]
  (reduce (fn [res word]
            (update-in res [word] (fnil inc 0)))
          {} coll))

(def sort-map (partial sort-by (comp - val)))

(defn word-freqs
  ([file]
     (word-freqs file 10))
  ([file n]
     (->> file
          get-lines
          get-words
          lowercase-words
          remove-stop-words
          count-freqs
          sort-map
          (take n))))