Re: [Boost-users] [mapreduce] Prim Calculator

Subject: Re: [Boost-users] [mapreduce] Prim Calculator
From: Christian Henning (chhenning_at_[hidden])
Date: 2009-08-21 10:04:58

Hi Craig, what you're suggesting is exactly what I do. For reasons I
don't understand I'm getting the following assertion:

Running Parallel Prime_Calculator MapReduce...Assertion failed:
map_key != typename map_task_type::key_type(), file
c:\chh\boost\boost\mapreduce\job.hpp, line 210

I don't understand why that happens? Can you help me out here.

Thanks,
Christian

On Thu, Aug 20, 2009 at 6:09 PM, Craig
Henderson<cdm.henderson_at_[hidden]> wrote:
>> Hi Craig, I did my best in translating the is_prime problem into a
>> map_reduce solution. The problem is simple: Find all prime numbers for
>> a given range of numbers, for instance, 0...1,000. Below is the source
>> code that I came up with. I cannot attach files from my work, so,
>> please excuse the bad formatting.
>>
>> The map function takes a number and emits a key/value pair of (
>> size_t, number ). The size_t key basically states weather or not a the
>> number is prime. I don't quite understand how do the reduce function?
>> I can see that in your word count example you accumulate the same
>> words to calculate the count. What I want is to pushing back the prime
>> numbers into a vector that I can print out at the end of program.
>
> The generic form of Map/Reduce maps a key/value pair k1,v1 to a list of
> key/value pairs k2,v2. The reduce then takes a group of v2 values for each
> unique key k2 and produces a final list of v2
>
> map    (k1, v1)       --> list(k2,v2)
> reduce (k2, list(v2)) --> list(v2)
>
> Your input is a list of unique integers, k1, and v1 is unused. Map emits
> intermediates where k2 is 0 or 1, indicating prime or not prime and v2 is
> the number (copied from k1). The Reduce function should then emit v2 if k2
> is 1 and do nothing if k2 is 0. This will result in the final dataset
> containing prime numbers.
>
> i.e.
> map(1,2,3,4,5,6) --> ((1,1), (1,2), (1,3), (0,4), (1,5), (0,6))
> reduce(1, (1,2,3,5)) --> (1,2,3,5)
> reduce(0, (4,6)) --> null
>
> I'll take a look at your code tomorrow and try and supply you a working
> example. If you get it working in the meantime, let me know.
>
> Regards
> -- Craig
>
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