Python Reduce Function

Python Reduce Function

reduce()

reduce(function, iterable[, initial]) -> value

Apply a function of two arguments cumulatively to the items of a sequence or iterable, from left to right, so as to reduce the iterable to a single value. For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates ((((1+2)+3)+4)+5). If initial is present, it is placed before the items of the iterable in the calculation, and serves as a default when the iterable is empty.

Here is an example that makes use of reduce to find the column value corresponding to the column letters that we see in the spreadsheets.

In this sample, first function does not use the reduce method. Second one does use it.

from functools import reduce
def column_id(s):
    return reduce(lambda result,c: result *26 + ord(c) - ord('A')+1,s,0)

print(column_id('CA'))
print(column_id('D'))
print(column_id('ZZ'))


def get_ord(s):
    result = 0
    for c in s:
        result = result *26 + ord(c) - ord('A') + 1
    return result

print(get_ord('CA'))
print(get_ord('D'))
print(get_ord('ZZ'))

(base) pradeep:~$/usr/local/bin/python3 /Users/pradeep/LearnPython/ftools.py
79
4
702
79
4
702
(base) pradeep:~$

We can see combining lamda with reduce simplifies the code a lot.