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Numpy Beginner's Guide (Update)

You're reading from   Numpy Beginner's Guide (Update) Build efficient, high-speed programs using the high-performance NumPy mathematical library

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Product type Paperback
Published in Jun 2015
Publisher
ISBN-13 9781785281969
Length 348 pages
Edition 1st Edition
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Author (1):
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Ivan Idris Ivan Idris
Author Profile Icon Ivan Idris
Ivan Idris
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Table of Contents (16) Chapters Close

Preface 1. NumPy Quick Start FREE CHAPTER 2. Beginning with NumPy Fundamentals 3. Getting Familiar with Commonly Used Functions 4. Convenience Functions for Your Convenience 5. Working with Matrices and ufuncs 6. Moving Further with NumPy Modules 7. Peeking into Special Routines 8. Assuring Quality with Testing 9. Plotting with matplotlib 10. When NumPy Is Not Enough – SciPy and Beyond 11. Playing with Pygame A. Pop Quiz Answers B. Additional Online Resources C. NumPy Functions' References
Index

Time for Action – clustering points

We will generate some random points and cluster them, which means that the points that are close to each other are put into the same cluster. This is just one of the many techniques that you can apply with scikit-learn. Clustering is a type of machine learning algorithm, which aims to group items based on similarities. Next, we will calculate a square affinity matrix. An affinity matrix is a matrix containing affinity values: for instance, the distances between points. Finally, we will cluster the points with the AffinityPropagation class from scikit-learn.

  1. Generate 30 random point positions within a square of 400 by 400 pixels:
    positions = np.random.randint(0, 400, size=(30, 2))
  2. Calculate the affinity matrix using the Euclidean distance to the origin as the affinity metric:
    positions_norms = np.sum(positions ** 2, axis=1)
    S = - positions_norms[:, np.newaxis] - positions_norms[np.newaxis, :] + 2 * np.dot(positions, positions.T)
  3. Give the AffinityPropagation...
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