On Mon, Oct 27, 2008 at 11:31 AM, Rich Hickey <[EMAIL PROTECTED]> wrote:
>
>
>
> On Oct 27, 12:04 pm, "Bill Clementson" <[EMAIL PROTECTED]> wrote:
>> Hi Chouser
>>
>> On Mon, Oct 27, 2008 at 8:46 AM, Chouser <[EMAIL PROTECTED]> wrote:
>>
>> > I think it's generally better to use = instead of .equals for
>> > equality, unless you have a specific reason to not use = (which I
>> > don't think is the case here).
>>
>> Only that it allowed me to talk about Java interop in my blog post. ;-)
>>
>>
>>
>> > On Mon, Oct 27, 2008 at 11:12 AM, Stuart Halloway
>> > <[EMAIL PROTECTED]> wrote:
>>
>> >> You could do something like this:
>>
>> >> (defn seq-xor-2-seqs
>> >> "Returns the unique values that are in one sequence but not the
>> >> other."
>> >> [x y]
>> >> (let [x (into #{} x)
>> >> y (into #{} y)]
>> >> (lazy-cat (clojure.set/difference x y)
>> >> (clojure.set/difference y x))))
>>
>> >> Not sure this is more idiomatic, though. And I guess it would perform
>> >> worse with huge collections...
>>
>> > If I'm reading thing's correctly, Bill's solution is O(n^2), while
>> > Stuart's is O(n*log(n)) or better. It looks like difference iterates
>> > over one seq and for each item does a lookup (nearly constant time) on
>> > the the other, although copying into sets may use more memory.
>>
>> > By the way, difference is eager, so I'm not sure there's much point in
>> > using lazy-cat. :-)
>>
>> > Here's another approach to do all the seqs at once:
>>
>> > (defn seq-xor
>> > "Returns unique values that are in one sequence but not the others."
>> > [& seqs]
>> > (let [obj-cnt (reduce (fn [acc s]
>> > (merge-with + acc (into {} (for [i s] {i 1}))))
>> > {} seqs)]
>> > (for [[obj cnt] obj-cnt :when (== cnt 1)]
>> > obj)))
>>
>> Oooh, very nice!
>>
>
> Here's a simple one with set ops:
>
> (alias 'set 'clojure.set)
>
> (defn set-xor [& sets]
> (second (reduce
> (fn [[all ret] s]
> [(set/union all s) (set/union (set/difference ret s)
> (set/difference s all))])
> [#{} #{}] sets)))
>
> (defn seq-xor [& seqs] (seq (apply set-xor (map set seqs))))
Yet another clever alternative!
Thanks guys!
- Bill
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