Python Numpy Lecture Notes

Introduction

• Presenter: Ivan Jetty
• Topic: Numpy and Multi-dimensional Arrays

Overview of Numpy

• Discussed previously about Numpy for 3-4 videos.
• Importance of multi-dimensionality in Numpy.

Multi-dimensional Arrays

Definition

• Multi-dimensional arrays can be one-dimensional, two-dimensional, or three-dimensional.

Creating a Two-Dimensional Array

• Syntax to create a two-dimensional array using nested arrays.
• Example:

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

Attributes of a 2D Array

• Dtype: Returns the type of data in the array.
• ndim: Returns the number of dimensions (for 2D array, it returns 2).
• shape: Returns tuple of (rows, columns); e.g., shape of the example array is (2, 3).
• size: Returns total number of elements (for example, 6).

Array Manipulation

Flattening a 2D Array

• Use .flatten() to convert 2D to 1D:

  arr1 = arr.flatten()
  

Reshaping Arrays

• Use .reshape() to convert 1D to 2D or 3D.
• Example of converting 1D to 2D:

  arr2 = arr1.reshape(3, 4)  # 3 rows, 4 columns
  

Creating a 3D Array

• Syntax example for creating a 3D array:

  arr3 = arr.reshape(2, 2, 3)
  

  • This creates 2 arrays, each containing 2 rows and 3 columns.

Matrices in Numpy

Concept of Matrices

• Matrices can be represented as 2D arrays.
• Use np.matrix() to convert a 2D array to a matrix for advanced operations.

  m = np.matrix(arr)
  

Operations with Matrices

• Diagonal elements can be accessed using .diagonal().
• Minimum and maximum values can be found using .min() and .max().
• Adding two matrices is straightforward.
• Multiplying matrices requires understanding of row and column combinations, done automatically in Python.

Summary

• Python simplifies array and matrix operations.
• Multiple functions are available in Numpy for efficient data manipulation.
• Encouragement to explore matrix multiplication manually for better understanding.

Conclusion

• Questions can be left in the comment section for further clarification.
• Encouragement to engage with the content and practice.