Python:NumPy .cumprod()

In NumPy, the .cumprod() method returns the cumulative product of the array elements over a particular axis. This method belongs to the ndarray class.

Syntax

ndarray.cumprod(axis=None, dtype=None, out=None)

Parameters:

• axis (optional): Axis along which the cumulative product is computed. The default (None) flattens the array.
• dtype (optional): The data type of the output array. Useful when input elements are of smaller types and may overflow.
• out (optional): An alternative output array where results will be stored. It must have the same shape as the expected output.

Return value:

Returns a new array that contains the cumulative product of elements along the specified axis. If out is provided, the result is placed into it.

Example 1: Cumulative Product of a 1D Array

This example computes the cumulative product of all elements in a one-dimensional array:

import numpy as np

a = np.array([1, 2, 3, 4])
print("Original array:", a)

result = a.cumprod()
print("Cumulative product:", result)

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The output of this code is:

Original array: [1 2 3 4]
Cumulative product: [ 1  2  6 24]

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Each element in the output represents the product of all elements up to that index in the input array.

Example 2: Cumulative Product Along Different Axes

This example shows how .cumprod() behaves when applied across rows and columns of a 2D array:

import numpy as np

b = np.array([[1, 2, 3],
              [4, 5, 6]])

print("Original array:")
print(b)

# Cumulative product along rows (axis=1)
row_cumprod = b.cumprod(axis=1)
print("\nCumulative product along rows (axis=1):")
print(row_cumprod)

# Cumulative product along columns (axis=0)
col_cumprod = b.cumprod(axis=0)
print("\nCumulative product along columns (axis=0):")
print(col_cumprod)

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The output of this code is:

Original array:
[[1 2 3]
 [4 5 6]]

Cumulative product along rows (axis=1):
[[  1   2   6]
 [  4  20 120]]

Cumulative product along columns (axis=0):
[[ 1  2  3]
 [ 4 10 18]]

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• When axis=1, the cumulative product is computed across each row.
• When axis=0, it’s computed down each column.

Codebyte Example

Run this interactive example to experiment with .cumprod() on a 2D array:

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