partition_while.clj

(defn partition-while
  "partitions elements in order while the predicate function holds
   the predicate function is given the current element
   and the current partition. "
  [f coll]
  (loop [truck [] box [] [book & books] coll]
    (if (empty? books)                            ; if there are no more books to pack
      (conj truck box)                            ; tape up the last box, put it in the truck, and return the truck
      (if (f book box)                            ; otherwise, if we can put the current book in the pending box
        (recur truck (conj box book) books)       ; put the book in the box and work on the next book
        (recur (conj truck box) [book] books))))) ; otherwise, tape up the box, put it in the truck, and start a new box with the new book in it, and work on the next book

(def words ["or" "line" "important" "may" "life" "mountain" "went"
  "change" "along" "water" "through" "just" "look" "because" "than" "into"
  "three" "after" "does" "stop" "get" "eye" "small" "world" "carry" "play"
  "all" "really" "before" "don't" "family" "river" "enough" "another" "came"
  "number" "why" "might" "write" "must" "other" "air" "something" "even" "own"
  "children" "in" "keep" "saw" "kind" "see" "without" "country" "left" "night"
  "story" "about" "but" "cut" "at" "few" "question" "began" "almost" "let" "put"
  "again" "side" "good" "four" "always" "mile" "soon" "know" "man" "should"
  "live" "begin" "more"])

(partition-while #(< (+ (count %1) (apply + (map count %2))) 15) words) ;; partition into subsequences of no more than 14 characters
;; [["or" "line"] ["important" "may"] ["life" "mountain"] ["went" "change"]
;;  ["along" "water"] ["through" "just"] ["look" "because"] ["than" "into" "three"]
;;  ["after" "does" "stop"] ["get" "eye" "small"] ["world" "carry" "play"]
;;  ["all" "really"] ["before" "don't"] ["family" "river"] ["enough" "another"]
;;  ["came" "number" "why"] ["might" "write" "must"] ["other" "air"]
;;  ["something" "even"] ["own" "children" "in"] ["keep" "saw" "kind" "see"]
;;  ["without" "country"] ["left" "night" "story"] ["about" "but" "cut" "at"]
;;  ["few" "question"] ["began" "almost" "let"] ["put" "again" "side"]
;;  ["good" "four" "always"] ["mile" "soon" "know"] ["man" "should" "live"] ["begin"]]

(defn count-of-e [s] (count (filter #{\e} s)))
(partition-while (fn [elem part] (< (+ (count-of-e elem) (reduce + (map count-of-e part))) 5)) words) ;; make sure no partition has more than 4 e's

;; [["or" "line" "important" "may" "life" "mountain" "went" "change" "along"]
;;  ["water" "through" "just" "look" "because" "than" "into"]
;;  ["three" "after" "does" "stop"]
;;  ["get" "eye" "small" "world" "carry" "play" "all" "really"]
;;  ["before" "don't" "family" "river" "enough"]
;;  ["another" "came" "number" "why" "might" "write" "must"]
;;  ["other" "air" "something" "even" "own"]
;;  ["children" "in" "keep" "saw" "kind"]
;;  ["see" "without" "country" "left" "night" "story" "about" "but" "cut" "at" "few"]
;;  ["question" "began" "almost" "let" "put" "again" "side" "good" "four" "always"]
;;  ["mile" "soon" "know" "man" "should" "live" "begin"]]

if you don't like the nested ifs, cond is an option too. decide for yourself:

(defn partition-while
  [f coll]
  (loop [truck []
         box [] 
         [book & books] coll]
    (cond 
      (empty? books) (conj truck box) 
      (f book box)   (recur truck (conj box book) books)
      :else          (recur (conj truck box) [book] books))))