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MapReduce, mail # user - Doubt on Input and Output Mapper - Key value pairs


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Re: Doubt on Input and Output Mapper - Key value pairs
Mahesh Balija 2012-11-08, 05:53
Hi Rams,

           A mapper will accept single key-value pair as input and can emit
0 or more key-value pairs based on what you want to do in mapper function
(I mean based on your business logic in mapper function).
           But the framework will actually aggregate the list of values
associated with a given key and sends the key and List of values to the
reducer function.

Best,
Mahesh Balija.

On Wed, Nov 7, 2012 at 6:09 PM, Ramasubramanian Narayanan <
[EMAIL PROTECTED]> wrote:

> Hi,
>
> Which of the following is correct w.r.t mapper.
>
> (a) It accepts a single key-value pair as input and can emit any number of
> key-value pairs as output, including zero.
> (b) It accepts a single key-value pair as input and emits a single key and
> list of corresponding values as output
>
>
> regards,
> Rams
>