learn-python/contrib/numpy/array-iteration.md

NumPy Array Iteration

Iterating over arrays in NumPy is a common task when processing data. NumPy provides several ways to iterate over elements of an array efficiently. Understanding these methods is crucial for performing operations on array elements effectively.

1. Basic Iteration

• Iterating using basic for loop.

Single-dimensional array

Iterating over a single-dimensional array is straightforward using a basic for loop

import numpy as np

arr = np.array([1, 2, 3, 4, 5])
for i in arr:
    print(i)

Output

1
2
3
4
5

Multi-dimensional array

Iterating over multi-dimensional arrays, each iteration returns a sub-array along the first axis.

marr = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

for arr in marr:
    print(arr)

Output

[1 2 3]
[4 5 6]
[7 8 9]

2. Iterating with nditer

• nditer is a powerful iterator provided by NumPy for iterating over multi-dimensional arrays.
• In each interation it gives each element.

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6]])
for i in np.nditer(arr):
    print(i)

Output

1
2
3
4
5
6

3. Iterating with ndenumerate

• ndenumerate allows you to iterate with both the index and the value of each element.
• It gives index and value as output in each iteration

import numpy as np

arr = np.array([[1, 2], [3, 4]])
for index,value in np.ndenumerate(arr):
    print(index,value)

Output

(0, 0) 1
(0, 1) 2
(1, 0) 3
(1, 1) 4

4. Iterating with flat

• The flat attribute returns a 1-D iterator over the array.

import numpy as np

arr = np.array([[1, 2], [3, 4]])
for element in arr.flat:
    print(element)

Output

1
2
3
4

Understanding the various ways to iterate over NumPy arrays can significantly enhance your data processing efficiency.

Whether you are working with single-dimensional or multi-dimensional arrays, NumPy provides versatile tools to iterate and manipulate array elements effectively.