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Questions and Answers
What is the main assumption when generating candidate itemsets?
What is the main assumption when generating candidate itemsets?
- Items must be compared by their lengths.
- The order of items can be ignored.
- The items in an itemset are ordered. (correct)
- Itemsets can be unordered.
How is a candidate itemset of size k+1 created?
How is a candidate itemset of size k+1 created?
- By randomly selecting items from Lk.
- By joining two itemsets of size k that share the first k-1 items. (correct)
- By duplicating an itemset of size k.
- By merging two itemsets of different sizes.
When merging two itemsets, what is the condition regarding shared items?
When merging two itemsets, what is the condition regarding shared items?
- They must share all items for merging to occur.
- They do not need to share any items.
- They must share the first k-1 items. (correct)
- They can share only the last item.
Why is it important that the items are ordered in generating candidates?
Why is it important that the items are ordered in generating candidates?
Which of the following represents the correct example of merging two itemsets?
Which of the following represents the correct example of merging two itemsets?
What does a frequent itemset indicate when its support is greater than or equal to the minsup threshold?
What does a frequent itemset indicate when its support is greater than or equal to the minsup threshold?
In the context of mining frequent itemsets, what is meant by the term 'support'?
In the context of mining frequent itemsets, what is meant by the term 'support'?
How many possible itemsets can exist given 'd' distinct items?
How many possible itemsets can exist given 'd' distinct items?
What might an itemset with high frequency in a dataset potentially suggest?
What might an itemset with high frequency in a dataset potentially suggest?
Which of the following is a characteristic of a frequent itemset?
Which of the following is a characteristic of a frequent itemset?
How does lowering the minimum support threshold affect the frequent itemsets?
How does lowering the minimum support threshold affect the frequent itemsets?
What can happen if the dimensionality of the data set increases?
What can happen if the dimensionality of the data set increases?
What effect does the size of the database have on the Apriori algorithm?
What effect does the size of the database have on the Apriori algorithm?
Why does an increase in average transaction width affect frequent itemsets?
Why does an increase in average transaction width affect frequent itemsets?
What does 'implication' refer to in the context of association rules?
What does 'implication' refer to in the context of association rules?
What operation is performed to generate candidate itemsets Ck+1?
What operation is performed to generate candidate itemsets Ck+1?
In the SQL generation of candidates Ck+1, which condition ensures that the items are combined correctly?
In the SQL generation of candidates Ck+1, which condition ensures that the items are combined correctly?
Which itemset would NOT be generated as a candidate from self-joining L3={abc, abd, acd, ace, bcd}?
Which itemset would NOT be generated as a candidate from self-joining L3={abc, abd, acd, ace, bcd}?
In the example provided, what is the output of the self-join of L3 that results in {a, b, c, d}?
In the example provided, what is the output of the self-join of L3 that results in {a, b, c, d}?
What does L3 represent in the context of generating candidate itemsets?
What does L3 represent in the context of generating candidate itemsets?
How many times does the itemset {Beer, Diaper} appear in the provided count list?
How many times does the itemset {Beer, Diaper} appear in the provided count list?
What is the primary goal of generating candidates Ck+1 in the context of itemsets?
What is the primary goal of generating candidates Ck+1 in the context of itemsets?
Which of the following itemsets counts as a candidate for {Bread,Diaper,Milk}?
Which of the following itemsets counts as a candidate for {Bread,Diaper,Milk}?
Which of the following itemsets has a counter value incremented to 8?
Which of the following itemsets has a counter value incremented to 8?
What is the hash function used in the example?
What is the hash function used in the example?
Which itemset is NOT included in the candidate itemsets of length 3?
Which itemset is NOT included in the candidate itemsets of length 3?
In the context of the Hash Tree structure, which level of the tree corresponds to hashing on the first item?
In the context of the Hash Tree structure, which level of the tree corresponds to hashing on the first item?
What is the top level of the candidate hash tree for the itemsets?
What is the top level of the candidate hash tree for the itemsets?
What does the term 'Frequent Itemsets' refer to in the A-Priori algorithm?
What does the term 'Frequent Itemsets' refer to in the A-Priori algorithm?
What does the counting of itemsets in the dictionary achieve?
What does the counting of itemsets in the dictionary achieve?
Which of the following itemsets is paired with a count of 0?
Which of the following itemsets is paired with a count of 0?
How do you perform the subset operation using the hash tree?
How do you perform the subset operation using the hash tree?
Which itemset had its counter value incremented to 2?
Which itemset had its counter value incremented to 2?
What is the key operation when processing itemsets in the A-Priori algorithm?
What is the key operation when processing itemsets in the A-Priori algorithm?
Which of the following describes the structure of a hash tree?
Which of the following describes the structure of a hash tree?
Which process involves filtering the results of candidate itemsets?
Which process involves filtering the results of candidate itemsets?
What is the main purpose of the recursive generation of itemsets?
What is the main purpose of the recursive generation of itemsets?
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Study Notes
Frequent Itemset Mining
- Application: Identify patterns in large datasets, like frequent co-occurrences.
- Example: Finding "Brad" and "Angelina" together in many documents might indicate a relationship.
- Frequent Itemset: A collection of items appearing together in a dataset.
- Example: {Milk, Bread, Diaper}
- Support (): The frequency of an itemset's occurrence.
- Count: Number of transactions containing the itemset.
- Fraction: Percentage of transactions containing the itemset.
- Frequent Itemset: An itemset whose support is greater than or equal to a given minimum support threshold.
- Mining Frequent Itemsets Task: Identify all itemsets exceeding the minimum support threshold in a set of transactions.
- Problem Parameters:
- N: The number of transactions.
- d: The number of unique items.
- w: Maximum number of items in a transaction.
- Challenge: The number of possible itemsets grows exponentially with the number of items (2^d).
- Solution: Utilize efficient algorithms like Apriori to find frequent itemsets.
Apriori Algorithm
- Assumption: Items within an itemset are ordered.
- Candidate Generation (Ck+1): Creating itemsets of size k+1 from frequent itemsets of size k (Lk) by joining itemsets that share the first k-1 items.
- Example: Combining {abc, abd} in L3 to generate {abcd} in C4.
- Subset Operation using Hash Tree: A hash tree structure allows for efficient subset checking during candidate generation.
- Hash Function: Maps items to specific branches of the tree.
- Leafs: Store potential candidate itemsets.
- Benefits: Reduces computation and storage requirements.
Association Rule Mining
- Definition: Discovering rules that predict the occurrence of one set of items based on the presence of other items in a transaction.
- Example: "If a customer buys diapers, then they are also likely to buy beer."
- Key Point: Implication refers to co-occurrence, not causal relationships.
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