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MapReduce, mail # user - Null mapper?


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Re: Null mapper?
Tom White 2010-08-18, 21:31
On Mon, Aug 16, 2010 at 3:21 PM, David Rosenstrauch <[EMAIL PROTECTED]> wrote:
> On 08/16/2010 05:48 PM, Ted Yu wrote:
>>
>> No.
>>
>> On Mon, Aug 16, 2010 at 1:25 PM, David
>> Rosenstrauch<[EMAIL PROTECTED]>wrote:
>>
>>> Is it possible for a M/R job to have no mapper?  i.e.:
>>> job.setMapperClass(null)?  Or is it required that one at least use an
>>> "identity mapper" (i.e., plain vanilla
>>> org.apache.hadoop.mapreduce.Mapper)?
>>>
>>> Thanks,
>>>
>>> DR
>
> Um ...
>
> Sorry, but I'm not clear.  Which of the 2 questions were you answering "no"
> to?  :-)
>
> I'm guessing the first.?  i.e., I can't have a null mapper.  So then I need
> to supply a org.apache.hadoop.mapreduce.Mapper as a "no-op" mapper?

org.apache.hadoop.mapreduce.Mapper is the identity mapper: it simply
emits the key-value pairs it was passed. The old API equivalent is
org.apache.hadoop.mapred.lib.IdentityMapper, which is the default.

Tom

>
> Can you please clarify?
>
> Thanks,
>
> DR
>