<!--
title: optimize data structures
domain: data-systems
topic: Algorithms
language: Other
source: apache/spark
updated: 2025-07-25
url: https://awesomereviewers.com/reviewers/spark-optimize-data-structures/
-->

Choose appropriate data structures and algorithms to optimize computational complexity and performance. Consider the specific use case and access patterns when selecting between different approaches.

Key optimization opportunities:

1. **Use efficient data structures for lookups**: Replace linear searches with constant-time operations where possible. For example, convert `ArrayContains` operations on literal arrays to `InSet` operations for O(1) lookup instead of O(n).

2. **Choose appropriate collection types**: Use `Set[String]` with `contains()` for simple string matching instead of `Set[Regex]` when regex functionality isn't needed. This avoids unnecessary regex compilation overhead.

3. **Leverage built-in collection methods**: Use `Array.tabulate(size)(constructor)` instead of manual loops for array initialization, and `collection.zip(other).toMap` for efficient map construction.

4. **Consider algorithmic properties**: Be aware of algorithm limitations like XOR checksums having issues with duplicate values. Consider alternatives like combining sum + XOR or using hash functions like Fowler–Noll–Vo when order-independence and duplicate-handling are required.

5. **Select semantic-appropriate data structures**: Use `ExpressionSet` for deduplicating expressions by semantics rather than object equality when the logical meaning matters more than object identity.

Example transformation:
```scala
// Instead of O(n) array search:
case ArrayContains(arrayParam: Literal, col) =>
  // Linear search through array elements

// Use O(1) set lookup:
case ArrayContains(arrayParam: Literal, col) if arrayParam.value != null =>
  InSet(col, arrayParam.value.asInstanceOf[GenericArrayData].array.toSet)
```

This approach reduces computational complexity and improves performance, especially for frequently executed operations or large datasets.
