Thanks Jacob for the response. If I run the UDF on each tuple then how can I preserve the state of the rank variable. I mean the UDF won't be able to save the rank value between calls, right? Correct me if I am wrong in interpreting that the UDF would be invoked for each tuple.
What I am looking in my output is an additional column indicating the rank. Something like Hick 35 1 Jimmy 30 2 Jack 25 3 Tampa 22 4 Sam 20 5 Thanks. Arun On Tue, Apr 26, 2011 at 7:18 PM, Jacob Perkins <[email protected]>wrote: > The question is, do you need the entire relation all at once to assign a > rank? If so then map-reduce may not be the answer. If not, why not just > run the UDF on each tuple of the relation, one at a time, with a > projection? > > If you need some global information, such as the max and min score, then > you might look at the MAX and MIN operations. They do require a GROUP > ALL but are algebraic so it's not actually going to bring all the data > to one machine as it otherwise would. > > --jacob > @thedatachef > > > On Tue, 2011-04-26 at 19:07 -0700, Arun A K wrote: > > Hi > > > > I have the following input relation: > > Name Score > > Jack 25 > > Jimmy 30 > > Sam 20 > > Hick 35 > > Tampa 22 > > > > My goal is to rank the tuples by score. > > > > Pig script: > > > > sample_data = LOAD 'sample.txt' USING PigStorage() AS (name:chararray, > > score:int); > > sample_data_group = GROUP sample_data BY score; > > sample_data_count = FOREACH sample_data_group GENERATE group AS score, > > COUNT(sample_data.name) AS countVal; > > sample_data_order = ORDER sample_data_count BY score DESC; > > sample_data_group_all = GROUP sample_data_order all; > > sample_data_project = FOREACH sample_data_group_all GENERATE > > FLATTEN(myUDF.Rank(sample_data_order)); > > dump sample_data_project; > > > > Can someone please point me to a UDF example where a relation is read in > and > > iterated over all its tuples? I plan to iterate over the tuples and > assign a > > rank to each of them based on the score value. > > > > Is there any other way to generate rank? > > > > Thanks much. > > > > Arun > > >
