On Thu, Mar 29, 2012 at 12:18 AM, simon.T <simon.j....@gmail.com> wrote:
> The obvious way is like the following, which traverse the sequence 2 times.
> ...
The obvious way does not necessarily traverse the sequence twice. If
a sequence S satisfies the 'counted?' predicate, (count S) takes
constant time. In particular
user=> (counted? [:a :b :c])
true
user=> (counted? '(:a :b :c))
true
user=> (counted? {:a 1 :b 2 :c 3})
true
user=> (counted? #{:a :b :c})
true
The examples are stolen from:
http://clojuredocs.org/clojure_core/clojure.core/counted_q
So it is very likely that (/ (reduce + coll) (count coll)) will not
traverse 'coll' twice, and the natural way is the preferred way.
<Insert standard warning about premature optimization./>
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