map-apply-sum-exclusive.clj

(defn map-apply-sum-exclusive [f s]
  "Maps each element in s to the sum of f applied that element and all other elements in s"
  (map-indexed
   (fn [i item]
     (reduce (fn [sum x] (+ sum x))
             0
             (keep-indexed (fn [j other-item]
                             (when (not (= i j))
                               (f item other-item)))
                           s
                           )))
   s))

(map-sum-exclusive (fn [x y] (+ x y)) '(1 2 3))
;;  1 => (+ (+ 1 2) (+ 1 3))
;;  2 => (+ (+ 2 1) (+ 2 3))
;;  3 => (+ (+ 3 1) (+ 3 2))
;;  output is (7 8 9)