A possible implementation for https://groups.google.com/forum/#!topic/clojure/bouoMeogZyU

days-to-numbers.clj

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

(defn bool->int
  [bool]
  (if bool 1 0))

(defn single-char-days
  "Translate two-char representation of certain day to one"
  [days]
  (-> days
      (s/replace #"TH" "R")
      (s/replace #"SU" "N")))
  
(defn flag-roster-members
  "For an ordered roster of items, return a list of bool, indicating presence."
  [roster members]
  (map (set members) roster))

(def days-of-week [\M \T \W \R \F \S \N])

(defn flag-days-in-week
  "Change string of days in week like MTTH to [1 1 0 1 0 0 0]"
  [days]
  (->> days
       single-char-days
       (flag-roster-members days-of-week)
       (mapv bool->int)))