multiple map functions query

Dmitry Demeshchuk demeshchuk at gmail.com
Fri Oct 28 10:05:20 EDT 2011


Why do you need such a way?

If you have some certain list of operations to perform on each object,
you can just combine them inside a body of a single map function.

If this list is dynamic and may vary depending on a situation – you
can pass the list of functions to execute as the second parameter to
the map function.

On the contrary, reduce functions cannot be combined like that – you
generally need to gather all the results of a previous reduce to get a
consistent result of the next one. So, multiple reduce functions are
not just allowed, but sometimes even necessary.

On Fri, Oct 28, 2011 at 5:59 PM, Lyes zaiko <lyesjob at gmail.com> wrote:
> Hi all!
> I want to execute a mapreduce query, in erlang, that contains two map phases
> such that the Map2 function takes the result of the Map1 function as input.
> Is it possible and if, what must be the return value of each map phase
> Thank you!
> _______________________________________________
> riak-users mailing list
> riak-users at lists.basho.com
> http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
>
>



-- 
Best regards,
Dmitry Demeshchuk



More information about the riak-users mailing list