Struct DictionaryEncoding 

pub struct DictionaryEncoding { /* private fields */ }

Stores repeated strings efficiently by referencing them with integer codes.

Each unique string appears once in the dictionary. Values are stored as u32 indices pointing into that dictionary. Great for labels, categories, and other low-cardinality string columns.

Implementations

impl DictionaryEncoding

pub fn new(dictionary: Arc<[Arc<str>]>, codes: Vec<u32>) -> Self

Creates a new dictionary encoding from a dictionary and codes.

pub fn with_nulls(self, null_bitmap: Vec<u64>) -> Self

Creates a dictionary encoding with a null bitmap.

pub fn len(&self) -> usize

Returns the number of values.

pub fn is_empty(&self) -> bool

Returns whether the encoding is empty.

pub fn dictionary_size(&self) -> usize

Returns the number of unique strings in the dictionary.

pub fn dictionary(&self) -> &Arc<[Arc<str>]>

Returns the dictionary.

pub fn codes(&self) -> &[u32]

Returns the encoded values.

pub fn is_null(&self, index: usize) -> bool

Returns whether the value at index is null.

pub fn get(&self, index: usize) -> Option<&str>

Returns the string value at the given index.

Returns None if the value is null.

pub fn get_code(&self, index: usize) -> Option<u32>

Returns the code at the given index.

pub fn iter(&self) -> impl Iterator<Item = Option<&str>>

Iterates over all values, yielding Option<&str>.

pub fn compression_ratio(&self) -> f64

Returns the compression ratio (original size / compressed size).

A ratio > 1.0 means compression is effective.

pub fn encode(&self, value: &str) -> Option<u32>

Encodes a lookup value into a code, if it exists in the dictionary.

pub fn filter_by_code(&self, predicate: impl Fn(u32) -> bool) -> Vec<usize>

Filters the encoding to only include rows matching a predicate code.

Trait Implementations

impl Clone for DictionaryEncoding

fn clone(&self) -> DictionaryEncoding

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for DictionaryEncoding

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

Formats the value using the given formatter.