Struct FeatureHasher 

pub struct FeatureHasher { /* private fields */ }

Fixed-dimension feature hasher.

Uses two independent hash functions:

• The first determines the target bucket (hash1 % dimension).
• The second determines the sign (hash2 & 1) when signed = true.

The hash is deterministic given the same seed, ensuring reproducible output across runs.

Implementations

impl FeatureHasher

pub fn new(dimension: usize, seed: u64) -> Result<Self, RillError>

Create a new hasher with the given dimension and seed.

Uses signed hashing by default.

pub fn with_config(config: FeatureHasherConfig) -> Result<Self, RillError>

Create a new hasher with a custom configuration.

pub const fn dimension(&self) -> usize

The output dimension.

pub const fn seed(&self) -> u64

The random seed.

pub const fn signed(&self) -> bool

Whether signed hashing is enabled.

pub fn hash_string(&self, name: &str) -> FeatureId

Hash a string feature name to a FeatureId.

pub fn hash_strings( &self, pairs: &[(&str, f64)], ) -> Result<SparseFeatures, RillError>

Create SparseFeatures from string name/value pairs.

Each string is hashed to a FeatureId, then the pairs are sorted and duplicates are merged by summing values.

pub fn transform( &self, features: &SparseFeatures, ) -> Result<Vec<f64>, RillError>

Transform SparseFeatures into a dense Vec<f64>.

Each feature’s value is added to its target bucket (multiplied by the sign if signed hashing is enabled). Collisions cause values to accumulate.

Trait Implementations

impl Clone for FeatureHasher

fn clone(&self) -> FeatureHasher

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FeatureHasher

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.