How to use Python reduce()

Python provides 3 useful global functions we can use to work with collections: map(), filter() and reduce().

Tip: sometimes list comprehensions make more sense and are generally considered more pythonic

reduce() is used to calculate a value out of a sequence, like a list.

For example suppose you have a list of expenses, stored as tuples, and you want to calculate the sum of a property property in each tuple, in this case the cost of each expense:

expenses = [
    ('Dinner', 80),
    ('Car repair', 120)
]

You could iterate with a loop over them:

sum = 0
for expense in expenses:
    sum += expense[1]

print(sum) # 200

Or, you can use reduce() to reduce the list to a single value:

from functools import reduce

print(reduce(lambda a, b: a[1] + b[1], expenses)) # 200

reduce() is not available by default like map() and filter(). You need to import it from the standard library module functools.


This content originally appeared on flaviocopes.com and was authored by flaviocopes.com

Python provides 3 useful global functions we can use to work with collections: map(), filter() and reduce().

Tip: sometimes list comprehensions make more sense and are generally considered more pythonic

reduce() is used to calculate a value out of a sequence, like a list.

For example suppose you have a list of expenses, stored as tuples, and you want to calculate the sum of a property property in each tuple, in this case the cost of each expense:

expenses = [
    ('Dinner', 80),
    ('Car repair', 120)
]

You could iterate with a loop over them:

sum = 0
for expense in expenses:
    sum += expense[1]

print(sum) # 200

Or, you can use reduce() to reduce the list to a single value:

from functools import reduce

print(reduce(lambda a, b: a[1] + b[1], expenses)) # 200

reduce() is not available by default like map() and filter(). You need to import it from the standard library module functools.


This content originally appeared on flaviocopes.com and was authored by flaviocopes.com


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