lance-arrow-scalar

A scalar type backed by Apache Arrow arrays with Ord, Hash, and Eq support.

Overview

ArrowScalar wraps a single-element Arrow array and provides comparison and hashing operations by leveraging Apache Arrow's OwnedRow representation. This ensures:

Correct total ordering for all Arrow types
Proper NaN handling for floating-point values
Consistent null ordering
O(1) comparisons via cached row bytes

Features

Eq, Ord, and Hash traits for Arrow scalar values
Support for all Arrow data types
Serde serialization/deserialization support
Zero-copy conversion from Arrow arrays

Usage

Add to your Cargo.toml:

[dependencies]
lance-arrow-scalar = "57.0.0"

Then use in your code:

use lance_arrow_scalar::ArrowScalar;

// Create from primitive types
let a = ArrowScalar::from(42i32);
let b = ArrowScalar::from(100i32);
assert!(a < b);

// Create from strings
let s1 = ArrowScalar::from("hello");
let s2 = ArrowScalar::from("world");
assert!(s1 < s2);

// Use in collections
use std::collections::HashMap;
let mut map = HashMap::new();
map.insert(ArrowScalar::from("key"), ArrowScalar::from(123));

Cross-Type Comparison

Comparing scalars of different data types produces an arbitrary but consistent ordering based on the underlying row bytes. This allows scalars to be used as keys in sorted collections regardless of type, though the ordering across types is not semantically meaningful.

Implementation Details