Example: Chaining map reduce jobs in Disco. See https://groups.google.com/forum/#!topic/disco-dev/gSSxTqX_rj0

CsvInnerJoiner.py

import sys
sys.path.append("/home/damian/disco/lib/")
from disco.core import Job, result_iterator
from disco.worker.classic.func import chain_reader
import csv, sys


class CsvInnerJoiner(Job):
    partitions = 2
    sort = True

    def map(self, row, params):
        yield row[0], row[1:]

    @staticmethod
    def map_reader(fd, size, url, params):
        reader = csv.reader(fd, delimiter=',')
        for row in reader:
            yield row

    #@staticmethod
    def reduce(self, rows_iter, out, params):
        from disco.util import kvgroup
        from itertools import chain
        #for url_key, descriptors in kvgroup(sorted(rows_iter)):
        for url_key, descriptors in kvgroup(rows_iter):
            merged_descriptors = list(chain.from_iterable(descriptors))
            print url_key,"_______",merged_descriptors
            if len(merged_descriptors) > 3:
                Alist = merged_descriptors[:merged_descriptors.index("B")]
                Blist = merged_descriptors[merged_descriptors.index("B"):]
                Alistlength = len(Alist)/3
                Blistlength = len(Blist)/3
                for i in range(Alistlength):
                    for j in range(Blistlength):
                        container = int(Alist[3*i+2])*int(Blist[3*j+2])
                        yield [Alist[3*i+1],Blist[3*j+1]],container
                        #out.add(Alist[3*i+1],[Blist[3*j+1],container])        

simple_innerjoin.py

import sys
sys.path.append("/home/damian/disco/lib/")
from disco.core import Job, result_iterator
from disco.worker.classic.func import chain_reader
import csv, sys


if __name__ == '__main__':
    input_filename = "input.csv"
    output_filename = "output.csv"
    if len(sys.argv) > 1:
        input_filename = sys.argv[1]
        if len(sys.argv) > 2:
            output_filename = sys.argv[2]

    from CsvInnerJoiner import CsvInnerJoiner
    from SumJob import SumJob
    
    job = CsvInnerJoiner().run(input=[input_filename])
    job = SumJob().run(input=job.wait())

    with open(output_filename, 'w') as fp:
        writer = csv.writer(fp)
        for url_key, descriptors in result_iterator(job.wait(show=True)):
            writer.writerow([url_key] + descriptors)

SumJob.py

import sys
sys.path.append("/home/damian/disco/lib/")
from disco.core import Job, result_iterator
from disco.worker.classic.func import chain_reader
import csv, sys


class SumJob(Job):
    map_reader = staticmethod(chain_reader)

    @staticmethod
    def map(key_value, params):
        print "KEY::::::",str(key_value[0])
        print "VAL::::::",str(key_value[1])
        yield key_value[0], key_value[1]
    @staticmethod    
    def reduce(key_value,out, params):
        Summe = sum(key_value[1])
        out.add(key_value[0],Summe)