Eclat Algorithm in Machine Learning

3 min readSep 12, 2023


The Eclat algorithm is a frequent itemset mining technique used in machine learning and data mining to discover patterns in transactional datasets. It is particularly useful for market basket analysis, where you want to find associations between items frequently bought together.

market basket analysis — eclat algorithm
Photo by Viki Mohamad on Unsplash

How Eclat Algorithm Works:

The Eclat algorithm, short for “Equivalence Class Clustering and Bottom-Up Lattice Traversal” is a depth-first search-based approach to find frequent itemsets. It relies on the concept of an “equivalence class” to reduce the search space efficiently.

Here’s how it works step by step:

  1. Transaction Database: Eclat starts with a transaction database, where each row represents a transaction, and each column represents an item. Each cell contains either a 1 (indicating the presence of an item in a transaction) or 0 (indicating absence).
  2. Itemset Generation: Initially, Eclat creates a list of single items as 1-itemsets. It counts the support (frequency) of each item in the database by scanning it once.
  3. Building Equivalence Classes: Eclat constructs equivalence classes by grouping transactions that share common items in their 1-itemsets. Equivalence classes reduce the number of potential itemset combinations to consider.
  4. Recursive Search: Eclat recursively explores larger itemsets by combining smaller ones. It does this by taking the intersection of equivalence classes of items. This step is similar to the join operation in the Apriori algorithm.
  5. Pruning: Eclat prunes infrequent itemsets at each step to reduce the search space, just like Apriori. If an itemset’s support falls below a predefined minimum support threshold, it is eliminated.
  6. Repeat: Steps 4 and 5 are repeated iteratively to find all frequent itemsets in the dataset.

Practical Example:

Let’s say you have a transactional dataset for a grocery store:

Transaction 1: {Milk, Bread, Eggs}

Transaction 2: {Milk, Bread, Diapers}

Transaction 3: {Milk, Beer, Chips}

Transaction 4: {Bread, Diapers, Beer, Chips}

Transaction 5: {Bread, Eggs, Beer}

Suppose you want to find frequent itemsets with a minimum support of 2 transactions.

  1. Initially, the 1-itemsets are {Milk}, {Bread}, {Eggs}, {Diapers}, {Beer}, {Chips}. Calculate their support.
  2. Construct equivalence classes:

{Milk}: Transaction 1, 2, 3

{Bread}: Transaction 1, 2, 4, 5

{Eggs}: Transaction 1, 5

{Diapers}: Transaction 2, 4

{Beer}: Transaction 3, 4, 5

{Chips}: Transaction 3, 4

3. Recursively generate larger itemsets:

{Milk, Bread}, {Milk, Eggs}, {Milk, Diapers}, {Milk, Beer}, {Milk, Chips}

{Bread, Eggs}, {Bread, Diapers}, {Bread, Beer}, {Bread, Chips}

{Eggs, Diapers}, {Eggs, Beer}

{Diapers, Beer}, {Diapers, Chips}

{Beer, Chips}

4. Prune itemsets with support less than 2.

5. Continue this process until no more frequent itemsets can be found.

Differences Between Eclat and Apriori:-

Data Structure:

  • Eclat uses a depth-first search approach and equivalence classes to reduce the search space.
  • Apriori uses a breadth-first search and candidate generation, which can be computationally expensive.


  • Eclat is often more memory-efficient than Apriori because it doesn’t need to generate candidate itemsets explicitly.
  • Apriori can suffer from the generation of a large number of candidates, especially when dealing with datasets with a high number of items.

Algorithm Complexity:

  • Eclat tends to be faster than Apriori in practice for dense datasets with low minimum support thresholds.
  • Apriori’s performance can degrade when the minimum support is low, as it generates many candidate itemsets.


  • Eclat can be more easily parallelized due to its depth-first nature.
  • Apriori’s breadth-first approach is less naturally parallelizable.

In summary, the Eclat algorithm is a depth-first frequent itemset mining technique that uses equivalence classes to efficiently find patterns in transactional datasets. It has some advantages over the Apriori algorithm, particularly in terms of memory efficiency and scalability, making it a valuable tool for association rule mining.