Simple MRjob script to count words from a TSV with data in the form "category\t[item1,item2,item3]".

CityReviews.py

#!/usr/bin/env python

from mrjob.job import MRJob
import json
import re

class CityReviews(MRJob):

  def mapper(self, _, line):
    line = re.sub(r'\[|\]| ', '', line)
    data = line.split('\t')
    yield data[0], [item for item in data[1].split(',')]

  def combiner(self, city, data):
    words = dict()
    for item in data:
      if item in words:
        words[item] += 1
      else:
        words[item] = 1
    yield city, words

  def reducer(self, city, counts):
    yield city, [word for word in counts]

if __name__ == '__main__':
  CityReviews.run()