On Friday, October 24, 2014 4:38:46 PM UTC-4, Fluid Dynamics wrote:
>
> On Friday, October 24, 2014 4:28:54 PM UTC-4, Fluid Dynamics wrote:
>>
>> On Friday, October 24, 2014 4:19:52 PM UTC-4, Fluid Dynamics wrote:
>>>
>>> (= s (distinct s)) looks to me like it should return true if it lacks
>>> duplicates, false if it has duplicates, and, due to how laziness and =
>>> work, short circuit as soon as any duplicate item is found.
>>>
>>> Your way sounds closer to how this version works:
>>>
>>> (defn dupes? [c]
>>> (->> c
>>> (frequencies)
>>> (vals)
>>> (apply max)
>>> (< 1)))
>>>
>>> which works (truthy when there are duplicates this time) but is less
>>> efficient. A low level method would be
>>>
>>> (loop [s (seq s) seen? #{}]
>>> (if s
>>> (let [f (first s)]
>>> (when-not (seen? f)
>>> (recur (next s) (conj seen? f))))
>>> true))
>>>
>>> That one also returns true on duplicates, and returns nil if there are
>>> none, and short circuits as soon as it sees a duplicate.
>>>
>>
> Correction: like (= s (distinct s)) the loop is falsey on duplicates.
>
> There is also a difference in the handling of the corner case of an empty
> collection. The loop and (= s (distinct s)) return true (no duplicates),
> which seems sensible. Both frequencies-using versions blow up, but you can
> put a (cons (Object.)) or a (cons ::sentinel) or such at the start of the
> transformation sequence to fix them.
>
And just sticking a 1 after apply max also works. :)
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