How Do I Check if Lists Share Any Items in Python?

Test if Lists Share Any Items in Python

Introduction

When working with multiple lists in Python, it's often necessary to determine if any elements overlap between those lists. This serves as a fundamental operation for various data analysis and manipulation tasks.

Short Answer

The recommended approach for testing list overlap in Python is to utilize the not set(a).isdisjoint(b) expression. It offers a generally efficient and concise method for this task.

Detailed Analysis

Method 1: Set Intersection

<code class="python">bool(set(a) & set(b))</code>

• Converts both lists to sets, then checks their intersection.
• Relatively slow, especially for large lists, as converting to sets consumes additional memory and time.

Method 2: Generator Expression with In Operator

<code class="python">any(i in a for i in b)</code>

• Iterates through one list and checks each element for membership in the other list.
• Fast when elements are near the beginning of the list but inefficient for lists without shared elements or when shared elements are at the end.

Method 3: Hybrid (Iteration and Set Membership)

<code class="python">a = set(a); any(i in a for i in b)</code>

• Converts one list to a set and iterates through the other list, checking membership in the set.
• Generally slower than other methods.

Method 4: Isdisjoint Method of Sets

<code class="python">not set(a).isdisjoint(b)</code>

• Utilizes the isdisjoint() method of sets to determine if two sets have any common elements.
• Fast and efficient for both shared and disjoint lists, especially when lists are of different sizes.

Performance Comparison

Performance tests reveal that not set(a).isdisjoint(b) excels in most cases, especially for large lists or situations where shared elements are sparse.

Conclusion

For testing list overlap in Python, consider using the not set(a).isdisjoint(b) expression as it provides a reliable, efficient, and versatile solution across varying list sizes and scenarios.

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