Python — Using reduce()

Importing reduce

To use reduce(), you need to import it from the functools module:

from functools import reduce

Example 1: Sum of Elements

Let's start with a simple example: calculating the sum of all elements in a list.

numbers = [1, 2, 3, 4, 5]

result = reduce(lambda x, y: x + y, numbers)

print(result)  

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15

Example 2: Product of Elements

Similarly, you can calculate the product of all elements in a list.

numbers = [1, 2, 3, 4, 5]

result = reduce(lambda x, y: x * y, numbers)

print(result)  

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120

Example 3: Finding the Maximum Element

You can use reduce() to find the maximum element in a list.

numbers = [1, 2, 3, 4, 5]

result = reduce(lambda x, y: x if x > y else y, numbers)

print(result)  

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5

Example 4: Concatenating Strings

You can use reduce() to concatenate a list of strings into a single string.

words = ["Hello", "World", "from", "Python"]

result = reduce(lambda x, y: x + " " + y, words)

print(result)  

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Hello World from Python

Example 5: Using an Initial Value

You can provide an initial value to reduce(). This initial value is placed before the items of the sequence in the calculation and serves as a default when the sequence is empty.

numbers = [1, 2, 3, 4, 5]

result = reduce(lambda x, y: x + y, numbers, 10)

print(result)  

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25

Example 6: Flattening a List of Lists

You can use reduce() to flatten a list of lists into a single list.

lists = [[1, 2, 3], [4, 5], [6, 7, 8]]

result = reduce(lambda x, y: x + y, lists)

print(result)  

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[1, 2, 3, 4, 5, 6, 7, 8]

Example 7: Finding the Greatest Common Divisor (GCD)

You can use reduce() with the gcd function from the math module to find the GCD of a list of numbers.

import math

numbers = [48, 64, 256]

result = reduce(math.gcd, numbers)

print(result) 

16

Example 8: Combining Dictionaries

You can use reduce() to combine a list of dictionaries into a single dictionary.

dicts = [{'a': 1}, {'b': 2}, {'c': 3}]

result = reduce(lambda x, y: {**x, **y}, dicts)

print(result)  

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{'a': 1, 'b': 2, 'c': 3}

Example 9: Custom Function with reduce()

You can also use a custom function with reduce(). Here's an example that calculates the sum of squares of elements in a list.

def sum_of_squares(x, y):

    return x + y**2

numbers = [1, 2, 3, 4]

result = reduce(sum_of_squares, numbers, 0)

print(result)  

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30