system-design-primer/solutions/system_design/sales_rank/sales_rank_mapreduce.py
2017-03-04 21:06:17 -08:00

78 lines
1.9 KiB
Python

# -*- coding: utf-8 -*-
from mrjob.job import MRJob
class SalesRanker(MRJob):
def within_past_week(self, timestamp):
"""Return True if timestamp is within past week, False otherwise."""
...
def mapper(self, _ line):
"""Parse each log line, extract and transform relevant lines.
Emit key value pairs of the form:
(foo, p1), 2
(bar, p1), 2
(bar, p1), 1
(foo, p2), 3
(bar, p3), 10
(foo, p4), 1
"""
timestamp, product_id, category, quantity = line.split('\t')
if self.within_past_week(timestamp):
yield (category, product_id), quantity
def reducer(self, key, value):
"""Sum values for each key.
(foo, p1), 2
(bar, p1), 3
(foo, p2), 3
(bar, p3), 10
(foo, p4), 1
"""
yield key, sum(values)
def mapper_sort(self, key, value):
"""Construct key to ensure proper sorting.
Transform key and value to the form:
(foo, 2), p1
(bar, 3), p1
(foo, 3), p2
(bar, 10), p3
(foo, 1), p4
The shuffle/sort step of MapReduce will then do a
distributed sort on the keys, resulting in:
(category1, 1), product4
(category1, 2), product1
(category1, 3), product2
(category2, 3), product1
(category2, 7), product3
"""
category, product_id = key
quantity = value
yield (category, quantity), product_id
def reducer_identity(self, key, value):
yield key, value
def steps(self):
"""Run the map and reduce steps."""
return [
self.mr(mapper=self.mapper,
reducer=self.reducer),
self.mr(mapper=self.mapper_sort,
reducer=self.reducer_identity),
]
if __name__ == '__main__':
HitCounts.run()