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MapReduce, mail # user - How can I sort a file with pairs <Key Value> in reverse order?


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Re: How can I sort a file with pairs <Key Value> in reverse order?
Bhasker Allene 2013-06-11, 11:57
One way to approach is emit |Integer.MAX_VALUE - your key ||as output of
mapper.|
Example
Mapper input
7 vim
2 emacs
9 firefox

Mapper output
(Integer.MAX_VALUE - 7) vim
(Integer.MAX_VALUE - 2) emacs
(Integer.MAX_VALUE - 9) firefox

If you need secondary sorting on second part, you have to use composite
key  and write  your own petitioner, comparator.

Regards,
Bhasker

On 11/06/2013 11:10, Pedro S� da Costa wrote:
> I created a MapReduce job example that that uses the sort mechanism of
> hadoop to sort a file by the key in ascending order. This is an
> example of the data:
>
> 7    vim
> 2    emacs
> 9    firefox
>
> At the end, I get the result:
>
> 2    emacs
> 7    vim
> 9    firefox
>
>
>
> Now I want to sort in reverse order, for the result be:
> 9    firefox
> 7    vim
> 2    emacs
>
>
>
> How can I sort a file with pairs <Key Value> in reverse order?
>
> --
> Best regards,
--
Thanks & Regards,
Bhasker Allene