Indexing and Slicing in NumPy | Python Advanced Programming | Python Certification Training | Uplatz
https://training.uplatz.com/online-it... this Python NumPy tutorial by Uplatz, you will learn about Indexing and Slicing in NumPy.
In NumPy, indexing and slicing are essential techniques for accessing and extracting elements from multi-dimensional arrays (ndarrays). Understanding these concepts is crucial for effective data manipulation and analysis.
Here's an overview of indexing and slicing in NumPy:
1. Indexing: Indexing refers to accessing specific elements of an array using their positions. In NumPy, indexing starts at 0 for the first element, 1 for the second element, and so on. There are two primary types of indexing in NumPy:
a. Basic Indexing:
• For a one-dimensional array, indexing is straightforward. You can access individual elements using an integer index.
• For multi-dimensional arrays, you need to use multiple integers separated by commas to index elements in each dimension.
b. Boolean Indexing:
• NumPy allows indexing using Boolean arrays, which are arrays of the same shape as the original array, containing True or False values based on a condition.
• When indexing with Boolean arrays, only the elements corresponding to True values are selected.
2. Slicing: Slicing allows you to extract a portion (subarray) of an array by specifying a range of indices. The basic syntax for slicing is start:stop:step, where start is the index of the first element to include, stop is the index of the first element to exclude, and step determines the spacing between elements.
• If start is not specified, slicing starts from the beginning (index 0).
• If stop is not specified, slicing goes up to the end of the array.
• If step is not specified, the default value is 1.
Examples of Indexing and Slicing in NumPy:
import numpy as np
Creating a one-dimensional array
arr1d = np.array([1, 2, 3, 4, 5])
Indexing
print(arr1d[0]) # Output: 1 (accessing the first element)
print(arr1d[3]) # Output: 4 (accessing the fourth element)
Slicing
print(arr1d[1:4]) # Output: [2 3 4] (slicing from index 1 to index 3)
Creating a two-dimensional array
arr2d = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
Indexing
print(arr2d[0, 1]) # Output: 2 (accessing element at row 0, column 1)
Slicing
print(arr2d[:2, 1:]) # Output: [[2 3], [5 6]] (slicing rows 0 to 1 and columns 1 to end)
Indexing and slicing can also be used with Boolean arrays, enabling powerful data filtering and selection capabilities in NumPy. These techniques are widely used in data analysis, machine learning, and scientific computing tasks.
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