Thanks for your help. Now I get it.
On 11 June 2013 14:21, Bhasker Allene <allene.bhas...@gmail.com> wrote: > Mapper Input > > 7 vim > 2 emacs > 9 firefox > > Mapper output ( new key = Integer.MAX_VALUE - key value) > 2147483640 vim > 2147483645 emacs > 2147483636 firefox > > Note :Integer.MAX_VALUE is 2147483647 (which would be 2^31 - 1) > > Hadoop will sort the records for you. > If you are using single reducer, reducer input would be > > 2147483636 firefox > 2147483640 vim > 2147483645 emacs > > reducer output ( this time subtract key from Integer.MAX_VALUE to get > back original value) > 9 firefox > 7 vim > 2 emacs > > > On 11/06/2013 13:05, Pedro Sá da Costa wrote: > > Even with your answer I can't see how can I sort the data in reverse > order. I forgot to mention that, the output result is produced by one > reduce task. This means that, at any point of the execution of the job, > the data must be grouped and sorted in descendent order. > > > On 11 June 2013 13:57, Bhasker Allene <allene.bhas...@gmail.com> wrote: > >> 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 Sá 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 >> >> > > > -- > Best regards, > > > -- > Thanks & Regards, > Bhasker Allene > > -- Best regards,
