Delete an item from a clojure vector using index

0
votes

I want to do something that looks similar to replace but performs different operation.
Using replace will create a new vector containing the corresponding value(s) of the index provided.

example

(replace [10 9 8 7 6] [0 4])     ;;=> [10 6]

My question now is that is there a way to create a new vector that will exclude the corresponding value(s) of the index provided? i.e delete the values of the index provided from the vector.

the code below is just an illustration. "some-function means something needs to be there"  
( 'some-function'   [10 9 8 7 6] [0 4])    ;;=> [9 8 7]
4
vectorreplaceclojure
Are you, as some answers suggest, deleting a subrange, always given by two indexes? Or, as others assume, are you providing a sequence of any number of indexes to delete the values of? - Thumbnail

4 Answers

1
votes

I don't know of a native function that does what you want. If you were working with Maps you could use dissoc.

You can write your own function to do this. Here is one way (of many) below.

(defn dissoc-vec
  ([v ks]
    (let [pred (set ks)
          replace-keys (->> (range (count v))
                            (remove #(pred %))
                            vec)]
      (replace v replace-keys))))
0
votes

check out subvec.

to achieve the exact function you want, you can do this:

(fn [coll [a b]]
  (subvec coll (inc a) b))
0
votes

You probably need https://github.com/clojure/core.rrb-vector

[...]clojure.core.rrb-vector/subvec, which produces a new vector containing the appropriate subrange of the input vector (in contrast to clojure.core/subvec, which returns a view on the input vector).

0
votes

You can do this with the sequence functions as follows: 

(defn remove-indexes [indexes coll]
  (->> coll
       (map-indexed vector)
       (remove (comp (set indexes) first))
       (map second)
       vec))

(remove-indexes [0 4] [10 9 8 7 6])
;[9 8 7]
  • I've switched the arguments around to correspond with core remove.
  • Since it works on any collection, you might omit the final vec.

A transducer version is probably a bit quicker: 

(defn remove-indexes [is v]
  (into [] 
        (comp (map-indexed vector)
              (remove (comp (set is) first))
              (map second))
        v))