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import sys
salesTotal = 0
oldKey = None
for line in sys.stdin:
data = line.strip().split("\t")
if len(data) != 2:
# Something has gone wrong. Skip this line.
continue
thisKey, thisSale = data
if oldKey and oldKey != thisKey:
print oldKey, "\t", salesTotal
oldKey = thisKey
salesTotal = 0
oldKey = thisKey
salesTotal += float(thisSale)
if oldKey != None:
print oldKey, "\t", salesTotal

The ";' isn't needed on line 13

"sys" needs to be imported at the beginning

sanoops commented Mar 10, 2014

import sys
salesTotal = 0.0
oldKey = None
dummy_Data=["Miami 12.34","Miami 99.07","Miami 55.07","NYC 88.97","NYC 33.56"]

for line in dummy_Data:
data = line.strip().split(" ")
if len(data) != 2:
# Something has gone wrong. Skip this line.
continue

thisKey, thisSale = data
if oldKey and oldKey != thisKey:
    print oldKey, ":", salesTotal
    oldKey = thisKey
    salesTotal = 0

oldKey = thisKey
salesTotal += float(thisSale)

if oldKey != None:
print oldKey, ":", salesTotal

reducer.py https://gist.github.com/sanoops/9471084

Would it be cleaner to store this info to dictionary? It would make it so you don't have to keep track of oldKey vs thisKey, also it will work if the sort is imperfect, but I'm not sure if there's any map reduce specific thing it would screw up

import sys

salesTotals = {}

for line in sys.stdin:
    data = line.strip().split("\t")
    if len(data) != 2:
        # Something has gone wrong. Skip this line.           
        continue

    store, sale = data
    salesTotals.setdefault(store, 0)
    salesTotals[store] += float(sale)

for store in salesTotals:
    print "{0}\t{1}".format(store, salesTotals[store])

digitalmacgyver commented Jan 23, 2017

Line 13:

if oldKey and oldKey != thisKey:

Would be better written with an explicit check against None:

if oldKey is not None and oldKey != thisKey:

As it is, this code malfunctions if given input where the key is the empty string, e.g.:

NY\t100
\t200
SF\t300

Will yield an output of:
SF:600

Can anyone explain what the below line does, I understand one part and i don't get the first condition.

"if oldkey and oldkey!=None"

I don't get what the first condition "if oldkey and" does...Thanks in Advance

Senthil

Hi @senthil1988

The sentence "if oldkey..." what tests is that the variable oldkey is assigned to some value and its type is different than NoneType.

It would be clear and easier to write "if oldKey is not None..." instead of "if oldkey..."

Regards!

wbl17 commented Jul 2, 2017

Just tested the code locally. To me, line 15 is not necessary, is it? In this example (and supposedly in general, with the keys sorted), when a new city gets processed, the assignment oldKey=thisKey will be done in line 18 anyway; setting totalSales=0 is necessary, though.

Happy coding!

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