Vectors are mostly for speed and maintaining value sequence order.
Try this => (vec (reverse [1 2 3]))
Not this => (apply vector (reverse [1 2 3]))
As an alternative you can do this => (into [] (reverse [1 2 3]))
You can always use mapv when calling fun for each coll object.
Try this => (mapv #(* 2 %) [1 2 3])
Not this => (apply vector (map (partial * 2) [1 2 3]))
Try this => (vec (reverse [1 2 3]))
Not this => (apply vector (reverse [1 2 3]))
As an alternative you can do this => (into [] (reverse [1 2 3]))
You can always use mapv when calling fun for each coll object.
Try this => (mapv #(* 2 %) [1 2 3])
Not this => (apply vector (map (partial * 2) [1 2 3]))
01.12.2013, 06:15, "Andy Smith" <the4thamig...@googlemail.com>:
--Hi,
I am trying to understand the manipulation of vectors from an efficiency point of view. For example if I want to reverse a vector I can do the following
(apply vector (reverse [1 2 3]))
My understanding is that reverse will create a new list object (3 2 1) then this will be used to construct a new vector object [3 2 1]. What can I use to construct a new vector directly instead of having the intermediate list object being constructed?
I have read about rseq as providing something like a reverse iterator to the same underlying vector, which may be a great solution in this case, but my question is really about the more general case of any function that manipulates a vector e.g. the following also returns a list rather than a vector as desired,
(map (partial * 2) [1 2 3])
again forcing me to use apply vector e.g.
(apply vector (map (partial * 2) [1 2 3]))
Why dont we have a version of map that returns a vector when given a vector? We can do this kind of thing in other languages with templates/generics why not clojure?
There is obviously some basic principle/understanding that I am missing here. This kind of thing surely cant be very efficient, can it?
Andy--
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