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Python Data Analysis, Second Edition

You're reading from   Python Data Analysis, Second Edition Data manipulation and complex data analysis with Python

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Product type Paperback
Published in Mar 2017
Publisher Packt
ISBN-13 9781787127487
Length 330 pages
Edition 2nd Edition
Languages
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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. Getting Started with Python Libraries FREE CHAPTER 2. NumPy Arrays 3. The Pandas Primer 4. Statistics and Linear Algebra 5. Retrieving, Processing, and Storing Data 6. Data Visualization 7. Signal Processing and Time Series 8. Working with Databases 9. Analyzing Textual Data and Social Media 10. Predictive Analytics and Machine Learning 11. Environments Outside the Python Ecosystem and Cloud Computing 12. Performance Tuning, Profiling, and Concurrency A. Key Concepts
B. Useful Functions C. Online Resources

Mean shift

Mean shift is another clustering algorithm that doesn't require an estimate for the number of clusters. It has been successfully applied to image processing. The algorithm tries to iteratively find the maxima of a density function. Before demonstrating mean shift, we will average the rain data on a day-of-the-year basis using a Pandas DataFrame. Create the DataFrame and average its data as follows:

df = pd.DataFrame.from_records(x.T, columns=['dates', 'rain']) 
df = df.groupby('dates').mean() 
 
df.plot() 

The following plot is the result:

Mean shift

Cluster the data with the mean shift algorithm as follows:

x = np.vstack((np.arange(1, len(df) + 1) , df.as_matrix().ravel())) 
x = x.T 
ms = cluster.MeanShift() 
ms.fit(x) 
labels = ms.predict(x) 

If we visualize the data with different line widths and shading for the three resulting clusters, the following figure is obtained:

Mean shift

As you can see, we have three clusters based on the average rainfall in mm on...

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