Map Reduce: Why does this code give the correct output for max but not min? - mapreduce

Question

I am testing some map reduce code in Ubuntu, python 2 with commmand:
cat testfile2 | ./mapper.py | sort | ./reducer.py
I get the correct output for max but not min, ever time I get the value 1 for min as though it hasn't changed from it's original value. Every single value 'value' is less than 1 so on the first iteration through the for loop min should change to the first value and then update the min on further iterations. Am I loosing my mind or is there a silly mistake in the code? Please help!
#!/usr/bin/python
import sys
def reducer():
max = 0
min = 1
old_tuple = ('foo', 'bar')
i = 0
for line in sys.stdin:
data = line.strip().split("\t")
if len(data) != 3:
continue
city, year, value = data
new_tuple = (city, year)
if old_tuple != new_tuple:
if i != 0:
print "{0}\t{1}\t{2}\t{3}".format(old_tuple[0], old_tuple[1], max, min)
max = 0
min = 1
i += 1
old_tuple = new_tuple
if min > value:
min = value
if max < value:
max = value
if old_tuple != ('foo', 'bar'):
print "{0}\t{1}\t{2}\t{3}".format(old_tuple[0], old_tuple[1], max, min)
if __name__ == '__main__':
reducer()
The output I get looks like so
Alert 2009 0.215236752 1
Winnipeg 2017 0.032557214 1

Answer 1

Firstly I was using min and max as variable names that are keywords. After changing
min => minimum
max => maximum
the output was still incorrect. The same problem actually. It was only after attempting to get the min and max in a more Pythonic way that I got it working. I'm new to Python so this may still be not the best most Pythonic way but the code below is at least getting the min and max values as needed.
#!/usr/bin/python
import sys
import math
def reducer():
list_ = []
old_tuple = ('foo', 'bar')
i = 0
for line in sys.stdin:
data = line.strip().split("\t")
if len(data) != 3:
continue
city, year, value = data
new_tuple = (city, year)
if old_tuple != new_tuple:
if i != 0:
print "{0}\t{1}\t{2}\t{3}".format(old_tuple[0], old_tuple[1], max(list_), min(list_))
list_ = []
i += 1
list_.append(value)
old_tuple = new_tuple
if old_tuple != ('foo', 'bar'):
print "{0}\t{1}\t{2}\t{3}".format(old_tuple[0], old_tuple[1], max(list_), min(list_))
if __name__ == '__main__':
reducer()