Doing it in the pig script is not feasible because pig doesn't have any
notion of sequentiality - to maintain it, you'd need to have access to
state that's shared globally by all the mappers and reducers. One way I can
think of doing this is to have a UDF that maintains state - perhaps it can
maintain a file that's NFS mounted/or in HDFS so that it's available on all
the task nodes; then any call to the UDF can update that file (atomically)
and return a 'row number' that you could associate with your current tuple.
Something like:
B = FOREACH A GENERATE $0, $1, $2, $3, MyUDFs.GETROWNUM() as rownum;
However, AFAIK, you'd be better off doing it in HBase - perhaps at the time
of record insert, you could also add a 'row number' into the record?
On 22 May 2012 12:43, Mohammad Tariq <donta...@gmail.com> wrote:
> Hi Abhinav,
>
> Thanks a lot for the valuable response..Actually I was thinking of
> doing the same thing, but being new to Pig I thought of asking it on
> the mailing list first..As far as the data is concerned, second column
> will always be in ascending order.But I don't think it will be of any
> help..I think whatever you have suggested here would be the
> appropriate solution..Although I would like to ask you one thing..Is
> it feasible to add that first column having count in my pig script or
> do I have to change the data in my Hbase table itself???If yes then
> how can I achieve it in my script??Many thanks.
>
> Regards,
> Mohammad Tariq
>
>
> On Tue, May 22, 2012 at 1:16 AM, Abhinav Neelam <abhinavroc...@gmail.com>
> wrote:
> > Hey Mohammad,
> >
> > You need to have sorting requirements when you say 'top 5' records.
> Because
> > relations/bags in Pig are unordered, it's natural to ask: 'top 5 by what
> > parameter?' I'm unfamiliar with HBase, but if your data in HBase has an
> > implicit ordering with say an auto-increment primary key, or an explicit
> > one, you could include that field in your input to Pig and then apply TOP
> > on that field.
> >
> > Having said that, if I understand your problem correctly, you don't need
> > TOP at all - you just want to process your input in groups of 5 tuples
> at a
> > time. Again, I can't think of a way of doing this without modifying your
> > input. For example, if your input included an extra field like this:
> > 1 18.98 2000 1.21 193.46 2.64 58.17
> > 1 52.49 2000.5 4.32 947.11 2.74 64.45
> > 1 115.24 2001 16.8 878.58 2.66 94.49
> > 1 55.55 2001.5 33.03 656.56 2.82 60.76
> > 1 156.14 2002 35.52 83.75 2.6 59.57
> > 2 138.77 2002.5 21.51 105.76 2.62 85.89
> > 2 71.89 2003 27.79 709.01 2.63 85.44
> > 2 59.84 2003.5 32.1 444.82 2.72 70.8
> > 2 103.18 2004 4.09 413.15 2.8 54.37
> >
> > you could do a group on that field and proceed. Even if you had a field
> > like 'line number' or 'record number' in your input, you could still
> > manipulate that field (say through integer division by 5) to use it for
> > grouping. In any case, you need something to let Pig bring together your
> 5
> > tuple groups.
> >
> > B = group A by $0;
> > C = FOREACH B { <do some processing on your 5 tuple bag A> ...
> >
> > Thanks,
> > Abhinav
> >
> > On 21 May 2012 23:03, Mohammad Tariq <donta...@gmail.com> wrote:
> >
> >> Hi Ruslan,
> >>
> >> Thanks for the response.I think I have made a mistake.Actually I
> >> just want the top 5 records each time.I don't have any sorting
> >> requirements.
> >>
> >> Regards,
> >> Mohammad Tariq
> >>
> >>
> >> On Mon, May 21, 2012 at 9:31 PM, Ruslan Al-fakikh
> >> <ruslan.al-fak...@jalent.ru> wrote:
> >> > Hey Mohammad,
> >> >
> >> > Here
> >> > c = TOP(5,3,a);
> >> > you say: take 5 records out of a that have the biggest values in the
> >> third
> >> > column. Do you really need that sorting by the third column?
> >> >
> >> > -----Original Message-----
> >> > From: Mohammad Tariq [mailto:donta...@gmail.com]
> >> > Sent: Monday, May 21, 2012 3:54 PM
> >> > To: user@pig.apache.org
> >> > Subject: How to use TOP?
> >> >
> >> > Hello list,
> >> >
> >> > I have an Hdfs file that has 6 columns that contain some data stored
> in
> >> an
> >> > Hbase table.the data looks like this -
> >> >
> >> > 18.98 2000 1.21 193.46 2.64 58.17
> >> > 52.49 2000.5 4.32 947.11 2.74 64.45
> >> > 115.24 2001 16.8 878.58 2.66 94.49
> >> > 55.55 2001.5 33.03 656.56 2.82 60.76
> >> > 156.14 2002 35.52 83.75 2.6 59.57
> >> > 138.77 2002.5 21.51 105.76 2.62 85.89
> >> > 71.89 2003 27.79 709.01 2.63 85.44
> >> > 59.84 2003.5 32.1 444.82 2.72 70.8
> >> > 103.18 2004 4.09 413.15 2.8 54.37
> >> >
> >> > Now I have to take each record along with its next 4 records and do
> some
> >> > processing(for example, in the first shot I have to take records 1-5,
> in
> >> the
> >> > next shot I have to take 2-6 and so on)..I am trying to use TOP for
> this,
> >> > but getting the following error -
> >> >
> >> > 2012-05-21 17:04:30,328 [main] ERROR org.apache.pig.tools.grunt.Grunt
> >> > - ERROR 1200: Pig script failed to parse:
> >> > <line 6, column 37> Invalid scalar projection: parameters : A column
> >> needs
> >> > to be projected from a relation for it to be used as a scalar Details
> at
> >> > logfile: /home/mohammad/pig-0.9.2/logs/pig_1337599211281.log
> >> >
> >> > I am using following commands -
> >> >
> >> > grunt> a = load 'hbase://logdata'
> >> >>> using org.apache.pig.backend.hadoop.hbase.HBaseStorage(
> >> >>> 'cf:DGR cf:HD cf:POR cf:RES cf:RHOB cf:SON', '-loadKey true') as
> (id,
> >> >>> DGR, HD, POR, RES, RHOB, SON);
> >> > grunt> b = foreach a { c = TOP(5,3,a);
> >> >>> generate flatten(c);
> >> >>> }
> >> >
> >> > Could anyone tell me how to achieve that????Many thanks.
> >> >
> >> > Regards,
> >> > Mohammad Tariq
> >> >
> >>
> >
> >
> >
> > --
> > Hacking is, and always has been, the Holy
> > Grail of computer science.
>
--
Hacking is, and always has been, the Holy
Grail of computer science.
