Hi Ghislain,
I completely agree with your assessment. I would expect the two writings…
$map?*
map:for-each($map, function($key, $value) { $value })
…to be faster than…
$key ! map:get($map, $key)
$key ! $map($key)
…because the latter ones require one additional lookup per key.
However, from a practical perspective, this is mostly up to the
implementation, which may choose different evaluation strategies for
each of the alternatives. For example, the evaluation of $map?* or
$map($key) could possibly be sped if it can statically be detected
that $map will always be of type map(*).
All the best,
Christian
On Mon, Jul 17, 2017 at 8:31 AM, Ghislain Fourny <gfou...@inf.ethz.ch> wrote:
> Hi,
>
> My first (naive) thought reading this thread is that, from a theoretical
> complexity perspective -- unless I missed something -- the first version in
> the original message was already asymptotically optimal (linear). The time it
> takes to compute an output always has, as a lower bound, the time it takes to
> output it ("print it out"), and the output is made of two "passes of the
> input". The improvements suggested should change the constant, but
> asymptotically on larger inputs, I do not expect a significant difference.
>
> Having said this, of course, in practice, the constant may make a big
> difference.
>
> Just my two cents!
>
> Kind regards,
> Ghislain
>
>
>> On 16 Jul 2017, at 23:58, Michael Kay <m...@saxonica.com> wrote:
>>
>> ce between C and Assembly is a lot smaller than between C and XQ, and I
>> think memory management should not be taken lightly (I'm not saying you do).
>> In OP's case, I believe keys could be discarded while memory layout remains
>> intact.
>>
>>
>> As a general rule of thumb, a lower-level language performs better provided
>> that you have the time and skills to write the code efficiently.
>>
>> And as a general rule of thumb, you don't.
>>
>> Even when you are quite convinced that you do.
>>
>> It's a long time since I wrote in anything as low-level as C or assembler,
>> but if you compare XQuery and Java, the level of abstraction of the API for
>> maps is very similar, so there is no intrinsic reason to believe one should
>> perform better than the other. The main difference is that maps in XQuery
>> are immutable, which means you pay a little more for some operations (like
>> adding a new entry), and you pay a lot less for other operations (llike bulk
>> copying).
>>
>> Michael Kay
>> Saxonica
>> _______________________________________________
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>> http://x-query.com/mailman/listinfo/talk
>
>
> _______________________________________________
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