Find strings of length 3 which differ in one position

gistfile1.clj

(defn diff-by-1 [strings]
  (let [f (partition-by first (sort-by first strings))
        s (partition-by second (sort-by second strings))
        l (partition-by last (sort-by last strings))
        fs (map #(partition-by second (sort-by second %)) f)
        fl (map #(partition-by last (sort-by last %)) f)
        sl (map #(partition-by last (sort-by last %)) s)
        all (concat fs fl sl)]
    (remove #(= (count %) 1) (apply concat all))))