(defn best-rest [data]
"data = binned version = a"
  (let [group-it0 (group-by data (- (ncol data) 1))
        group-it (map #(if (= (nrow %) 1) [%] %) group-it0)]
    (loop [g group-it results (transient [])]
      (if (empty? g)
	      (persistent! results)
	      (recur (rest g)
	       (conj! 
		       results 
		       (vector (first g) 
			             (matrix 
			              (apply 
			                concat 
			                (filter #(not= (first g) %) group-it))))))))))