clojure - 从ref向量中删除一个元素

Question

I'm using a vector of maps which defined as a referece.

i want to delete a single map from the vector and i know that in order to delete an element from a vector i should use subvec .

my problem is that i couldn't find a way to implement the subvec over a reference vector. i tried to do it using: (dosync (commute v assoc 0 (vec (concat (subvec @v 0 1) (subvec @v 2 5))))) , so that the seq returned from the vec function will be located on index 0 of the vector but it didn't work.

does anyone have an idea how to implement this?

thanks

Answer 1

commute (just like alter ) needs a function that will be applied to the value of the reference.

So you will want something like:

;; define your ref containing a vector
(def v (ref [1 2 3 4 5 6 7]))

;; define a function to delete from a vector at a specified position
(defn delete-element [vc pos]
  (vec (concat 
         (subvec vc 0 pos) 
         (subvec vc (inc pos)))))

;; delete element at position 1 from the ref v
;; note that communte passes the old value of the reference
;; as the first parameter to delete-element
(dosync 
  (commute v delete-element 1))

@v
=> [1 3 4 5 6 7]

Note the that separating out the code to delete an element from the vector is a generally good idea for several reasons:

• This function is potentially re-usable elsewhere
• It makes your transaction code shorter and more self-desciptive