On Tue, 14 Jun 2005 07:19:09 -0700, Mark A. Biggar <[EMAIL PROTECTED]> wrote:
> Luke Palmer wrote:
>> On 14 Jun 2005 06:07:10 -0000, David Formosa (aka ? the Platypus)
>> <[EMAIL PROTECTED]> wrote:
>>>multi sub infix_circumfix_meta_operator:{'>>','<<'} (Hash %a,Hash %b,Code
>>>$op) {
>>> my Hash %return;
>>> for intersection(keys %a,keys %b) -> $key {
>>> %return{$key} = $op($a{$key},$b{$key});
>>> }
>>> return %return;
>>>}
>>>
>>> Would this be sensible, usefull behavour?
>>
[...] The difference between
>> the hyper hash ops and vector-vector ops in my class is the fact that
>> you did intersection instead of union (I assumed unset elements were
>> 0). Unfortunately, such an assumption doesn't make sense on a general
>> scale, so I wonder whether I would end up using the hash hyper ops or
>> whether I'd just go and implement them again.
>>
>> So, I'd really like to see a couple examples where this behavior could
>> be useful. I don't doubt that it can, but I can't think of anything
>> at the moment.
>
> This is effectively the Database inner vs outer join issue. There are
> times you need one and times you need the other. Example for the outer
> join case: combining two invoices where you want to add together the
> subtotals for each type of item and missing items on either invoice
> should be assumed to be 0 quantity at 0 dollars.
> Note that just like in
> the reduce op you need to know the identity value associated with the
> op. come to think of it just like in the DB world you really need 4
> different versions: inner join (intersection of keys), full outer join
> (union of keys) and the left and right outer joins where you on consider
> the missing keys on the left or right sides.
If you consider arrays to be hashes keyed by integers then @a >>..<<
@b does the equiverlent of an inner join. I would suggest that if we
are going to have outer join versions then we have something like this
>>...<< inner joing hyperop
>>>...<< left outer joing hyperop
>>...<<< right outer joing hyperop
>>>...<<< full outer joing hyperop
> This means that the current
> hyper-op should be define to be one of inner or full and we need some
> syntax to specify the other three op types. >>-:left<< Ugh!
I think my syntax is slightly less ugly.
--
Please excuse my spelling as I suffer from agraphia. See
http://dformosa.zeta.org.au/~dformosa/Spelling.html to find out more.
Free the Memes.
