Clojure Remove item from Vector at a Specified Location

Question

Is there a way to remove an item from a vector based on index as of now i am using subvec to split the vector and recreate it again. I am looking for the reverse of assoc for vectors?

Answer 1

subvec is probably the best way. The Clojure docs say subvec is "O(1) and very fast, as the resulting vector shares structure with the original and no trimming is done". The alternative would be walking the vector and building a new one while skipping certain elements, which would be slower.

Removing elements from the middle of a vector isn't something vectors are necessarily good at. If you have to do this often, consider using a hash-map so you can use dissoc.

Answer 2

user=> (def a [1 2 3 4 5])
user=> (time (dotimes [n 100000] (vec (concat (take 2 a) (drop 3 a)))))
"Elapsed time: 1185.539413 msecs"
user=> (time (dotimes [n 100000] (vec (concat (subvec a 0 2) (subvec a 3 5)))))
"Elapsed time: 760.072048 msecs"

Yup - subvec is fastest