A method for constructing incanter matrices in an easy fashion

matrix_rule.clj

;; enables you to define an incanter matrix (2-dimensional only) by a rule based on i j index

(defmacro matrix-rule [m index-rule application-fn]
   `(incanter/matrix 
      (into [] (for [i# (range 0 (incanter/nrow ~m))]
                  (into [] (for [j# (range 0 (incanter/ncol ~m))]
                              (if (~index-rule i# j#)
                                 (~application-fn i# j#)
                                 (incanter/sel ~m i# j#))))))))

(defn diagonal? [i j]
  (= i j))

(defn upper? [i j]
  (> j i))

(defn lower? [i j]
  (< j i))

;; best if used in a threaded way

(-> (incanter.core/matrix 0 3 3)
   (matrix-rule diagonal? (fn [i j] 5)) ;; make the diagonal 5
   (matrix-rule upper? (fn [i j] (+ i j))) ;; make the upper diagonal equal to i + j
   (matrix-rule lower? (fn [i j] (- i j)))) ;; make the lower diagonal equal to i - j