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Chapter 4 The classic algorithm for affinity analysis is called the Apriori algorithm. It addresses the exponential problem of creating sets of items that occur frequently within a database, called frequent itemsets. Once these frequent itemsets are discovered, creating association rules is straightforward. The intuition behind Apriori is both simple and clever. First, we ensure that a rule has sufficient support within the dataset. Defining a minimum support level is the key parameter for Apriori. To build a frequent itemset, for an itemset (A, B) to have a support of at least 30, both A and B must occur at least 30 times in the database. This property extends to larger sets as well. For an itemset (A, B, C, D) to be considered frequent, the set (A, B, C) must also be frequent (as must D). These frequent itemsets can be built up and possible itemsets that are not frequent (of which there are many) will never be tested. This saves significant time in testing new rules. Other example algorithms for affinity analysis include the Eclat and FP-growth algorithms. There are many improvements to these algorithms in the data mining literature that further improve the efficiency of the method. In this chapter, we will focus on the basic Apriori algorithm. Choosing parameters To perform association rule mining for affinity analysis, we first use the Apriori to generate frequent itemsets. Next, we create association rules (for example, if a person recommended movie X, they would also recommend movie Y) by testing combinations of premises and conclusions within those frequent itemsets. For the first stage, the Apriori algorithm needs a value for the minimum support that an itemset needs to be considered frequent. Any itemsets with less support will not be considered. Setting this minimum support too low will cause Apriori to test a larger number of itemsets, slowing the algorithm down. Setting it too high will result in fewer itemsets being considered frequent. In the second stage, after the frequent itemsets have been discovered, association rules are tested based on their confidence. We could choose a minimum confidence level, a number of rules to return, or simply return all of them and let the user decide what to do with them. In this chapter, we will return only rules above a given confidence level. Therefore, we need to set our minimum confidence level. Setting this too low will result in rules that have a high support, but are not very accurate. Setting this higher will result in only more accurate rules being returned, but with fewer rules being discovered. [ 63 ]
Recommending Movies Using Affinity Analysis The movie recommendation problem Product recommendation is big business. Online stores use it to up-sell to customers by recommending other products that they could buy. Making better recommendations leads to better sales. When online shopping is selling to millions of customers every year, there is a lot of potential money to be made by selling more items to these customers. Product recommendations have been researched for many years; however, the field gained a significant boost when Netflix ran their Netflix Prize between 2007 and 2009. This competition aimed to determine if anyone can predict a user's rating of a film better than Netflix was currently doing. The prize went to a team that was just over 10 percent better than the current solution. While this may not seem like a large improvement, such an improvement would net millions to Netflix in revenue from better movie recommendations. Obtaining the dataset Since the inception of the Netflix Prize, Grouplens, a research group at the University of Minnesota, has released several datasets that are often used for testing algorithms in this area. They have released several versions of a movie rating dataset, which have different sizes. There is a version with 100,000 reviews, one with 1 million reviews and one with 10 million reviews. The datasets are available from http://grouplens.org/datasets/movielens/ and the dataset we are going to use in this chapter is the MovieLens 1 million dataset. Download this dataset and unzip it in your data folder. Start a new IPython Notebook and type the following code: import os import pandas as pd data_folder = os.path.join(os.path.expanduser("~"), "Data", "ml-100k") ratings_filename = os.path.join(data_folder, "u.data") Ensure that ratings_filename points to the u.data file in the unzipped folder. Loading with pandas The MovieLens dataset is in a good shape; however, there are some changes from the default options in pandas.read_csv that we need to make. To start with, the data is separated by tabs, not commas. Next, there is no heading line. This means the first line in the file is actually data and we need to manually set the column names. [ 64 ]
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Learning Data Mining with Python Co
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About the Author Robert Layton has
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Christophe Van Gysel is pursuing a
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www.allitebooks.com
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Table of Contents Preprocessing usi
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Table of Contents Chapter 7: Discov
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Table of Contents GPU optimization
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Preface If you have ever wanted to
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What you need for this book It shou
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Preface Reader feedback Feedback fr
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Getting Started with Data Mining We
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Chapter 1 In the preceding dataset,
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After you have the above "Hello, wo
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Chapter 1 Windows users may need to
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Chapter 1 The dataset we are going
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Chapter 1 As an example, we will co
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Page 88 and 89: Chapter 4 When loading the file, we
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Page 94 and 95: Chapter 4 We want to break out the
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Page 104 and 105: Extracting Features with Transforme
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Discovering Accounts to Follow Usin
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Chapter 7 Next, we will need a list
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Chapter 7 Make sure the filename is
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Chapter 7 cursor = results['next_cu
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Chapter 7 Creating a graph Now, we
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Chapter 7 As you can see, it is ver
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Chapter 7 Next, we will only add th
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Chapter 7 We can graph the entire s
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Chapter 7 Optimizing criteria Our a
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Chapter 7 Next, we need to get the
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• method='nelder-mead': This is u
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Beating CAPTCHAs with Neural Networ
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Chapter 8 The red lines indicate th
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Chapter 8 The combination of an app
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Chapter 8 From these predictions, w
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Chapter 8 This code correctly predi
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The result is shown in the next gra
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Chapter 8 However, it isn't very go
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Chapter 8 Summary In this chapter,
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Authorship Attribution Attributing
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Authorship Attribution If we cannot
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Authorship Attribution After taking
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Authorship Attribution This dataset
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Authorship Attribution "instead", "
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Authorship Attribution Support vect
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Authorship Attribution Kernels When
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Authorship Attribution We can reuse
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Authorship Attribution With our dat
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Clustering News Articles In most of
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Chapter 10 API Endpoints are the ac
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The token object is just a dictiona
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Chapter 10 We then create a list to
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Chapter 10 We are going to use MD5
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Chapter 10 Next, we develop the cod
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Chapter 10 We use clustering techni
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Chapter 10 The k-means algorithm is
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Chapter 10 We only fit the X matrix
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Chapter 10 We then print out the mo
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Chapter 10 Our function definition
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Chapter 10 The result from the prec
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Chapter 10 Implementation Putting a
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Chapter 10 Neural networks can also
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We then call the partial_fit functi
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Classifying Objects in Images Using
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Chapter 11 This dataset comes from
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You can change the image index to s
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Chapter 11 Each of these issues has
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Chapter 11 Using Theano, we can def
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Chapter 11 Building a neural networ
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Chapter 11 Finally, we create Thean
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Chapter 11 return [image,] return s
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Chapter 11 Next, we define how the
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Chapter 11 Getting your code to run
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Chapter 11 Setting up the environme
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This will unzip only one Coval.otf
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Chapter 11 First we create the laye
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Chapter 11 Finally, we set the verb
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Chapter 11 Summary In this chapter,
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Working with Big Data Big data What
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Working with Big Data Governments a
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Working with Big Data Getting the d
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Working with Big Data If we aren't
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Working with Big Data Before we sta
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Working with Big Data The first val
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Working with Big Data Next, we crea
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Working with Big Data Left-click th
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Working with Big Data The result is
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Next Steps… Extending the IPython
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Next Steps… Chapter 3: Predicting
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Next Steps… Vowpal Wabbit http://
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Next Steps… Deeper networks These
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Next Steps… Real-time clusterings
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Next Steps… More resources Kaggle
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authorship, attributing 185-188 AWS
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feature extraction about 82 common
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NetworkX about 145 defining 303 URL
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scikit-learn package references 305
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Thank you for buying Learning Data
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Learning Python Data Visualization
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