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Fill positions in NgramTokenizer #2471

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Fill positions in NgramTokenizer #2471

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f90a800
Fill positions in NgramTokenizer
darashi Aug 6, 2024
94c4585
Fix format using `cargo +nightly fmt`
darashi Aug 29, 2024
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111 changes: 59 additions & 52 deletions src/tokenizer/ngram_tokenizer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,16 +3,12 @@ use crate::TantivyError;

/// Tokenize the text by splitting words into n-grams of the given size(s)
///
/// With this tokenizer, the `position` is always 0.
/// Beware however, in presence of multiple value for the same field,
/// the position will be `POSITION_GAP * index of value`.
///
/// Example 1: `hello` would be tokenized as (min_gram: 2, max_gram: 3, prefix_only: false)
///
/// | Term | he | hel | el | ell | ll | llo | lo |
/// |----------|-----|-----|-----|-----|-----|-----|----|
/// | Position | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
/// | Offsets | 0,2 | 0,3 | 1,3 | 1,4 | 2,4 | 2,5 | 3,5|
/// | Term | he | hel | el | ell | ll | llo | lo |
/// |----------|-----|-----|-----|-----|-----|-----|-----|
/// | Position | 0 | 0 | 1 | 1 | 2 | 2 | 3 |
/// | Offsets | 0,2 | 0,3 | 1,3 | 1,4 | 2,4 | 2,5 | 3,5 |
///
/// Example 2: `hello` would be tokenized as (min_gram: 2, max_gram: 5, prefix_only: **true**)
///
Expand All @@ -29,6 +25,14 @@ use crate::TantivyError;
/// | Position | 0 | 0 | 0 | 0 |
/// | Offsets | 0,3 | 0,4 | 0,5 | 0,6 |
///
/// Example 4: `hεllo` (non-ascii) would be tokenized as (min_gram: 2, max_gram: 3, prefix_only:
/// false)
///
/// | Term | hε | hεl | εl | εll | ll | llo | lo |
/// |----------|-----|-----|-----|-----|-----|-----|-----|
/// | Position | 0 | 0 | 1 | 1 | 2 | 2 | 3 |
/// | Offsets | 0,3 | 0,4 | 1,4 | 1,5 | 3,5 | 3,6 | 4,6 |
///
/// # Example
///
/// ```rust
Expand Down Expand Up @@ -161,11 +165,11 @@ impl Tokenizer for NgramTokenizer {

impl<'a> TokenStream for NgramTokenStream<'a> {
fn advance(&mut self) -> bool {
if let Some((offset_from, offset_to)) = self.ngram_charidx_iterator.next() {
if let Some((position, offset_from, offset_to)) = self.ngram_charidx_iterator.next() {
if self.prefix_only && offset_from > 0 {
return false;
}
self.token.position = 0;
self.token.position = position;
self.token.offset_from = offset_from;
self.token.offset_to = offset_to;
self.token.text.clear();
Expand Down Expand Up @@ -195,21 +199,23 @@ impl<'a> TokenStream for NgramTokenStream<'a> {
/// See `test_stutterring_iterator` for an example of its
/// output.
struct StutteringIterator<T> {
underlying: T,
underlying: std::iter::Enumerate<T>,
min_gram: usize,
max_gram: usize,

memory: Vec<usize>,
memory: Vec<(usize, usize)>,
cursor: usize,
gram_len: usize,
}

impl<T> StutteringIterator<T>
where T: Iterator<Item = usize>
{
pub fn new(mut underlying: T, min_gram: usize, max_gram: usize) -> StutteringIterator<T> {
pub fn new(underlying: T, min_gram: usize, max_gram: usize) -> StutteringIterator<T> {
assert!(min_gram > 0);
let memory: Vec<usize> = (&mut underlying).take(max_gram + 1).collect();
let mut underlying = underlying.enumerate();
let memory: Vec<(usize, usize)> = (&mut underlying).take(max_gram + 1).collect();
// let underlying = underlying.enumerate();
if memory.len() <= min_gram {
// returns an empty iterator
StutteringIterator {
Expand All @@ -236,9 +242,9 @@ where T: Iterator<Item = usize>
impl<T> Iterator for StutteringIterator<T>
where T: Iterator<Item = usize>
{
type Item = (usize, usize);
type Item = (usize, usize, usize);

fn next(&mut self) -> Option<(usize, usize)> {
fn next(&mut self) -> Option<(usize, usize, usize)> {
if self.gram_len > self.max_gram {
// we have exhausted all options
// starting at `self.memory[self.cursor]`.
Expand All @@ -258,10 +264,11 @@ where T: Iterator<Item = usize>
if self.max_gram < self.min_gram {
return None;
}
let start = self.memory[self.cursor % self.memory.len()];
let stop = self.memory[(self.cursor + self.gram_len) % self.memory.len()];

let (position, start) = self.memory[self.cursor % self.memory.len()];
let stop = self.memory[(self.cursor + self.gram_len) % self.memory.len()].1;
self.gram_len += 1;
Some((start, stop))
Some((position, start, stop))
}
}

Expand Down Expand Up @@ -367,13 +374,13 @@ mod tests {
assert_eq!(tokens.len(), 9);
assert_token(&tokens[0], 0, "h", 0, 1);
assert_token(&tokens[1], 0, "he", 0, 2);
assert_token(&tokens[2], 0, "e", 1, 2);
assert_token(&tokens[3], 0, "el", 1, 3);
assert_token(&tokens[4], 0, "l", 2, 3);
assert_token(&tokens[5], 0, "ll", 2, 4);
assert_token(&tokens[6], 0, "l", 3, 4);
assert_token(&tokens[7], 0, "lo", 3, 5);
assert_token(&tokens[8], 0, "o", 4, 5);
assert_token(&tokens[2], 1, "e", 1, 2);
assert_token(&tokens[3], 1, "el", 1, 3);
assert_token(&tokens[4], 2, "l", 2, 3);
assert_token(&tokens[5], 2, "ll", 2, 4);
assert_token(&tokens[6], 3, "l", 3, 4);
assert_token(&tokens[7], 3, "lo", 3, 5);
assert_token(&tokens[8], 4, "o", 4, 5);
}

#[test]
Expand All @@ -385,8 +392,8 @@ mod tests {
);
assert_eq!(tokens.len(), 3);
assert_token(&tokens[0], 0, "hel", 0, 3);
assert_token(&tokens[1], 0, "ell", 1, 4);
assert_token(&tokens[2], 0, "llo", 2, 5);
assert_token(&tokens[1], 1, "ell", 1, 4);
assert_token(&tokens[2], 2, "llo", 2, 5);
}

#[test]
Expand All @@ -413,13 +420,13 @@ mod tests {
assert_eq!(tokens.len(), 9);
assert_token(&tokens[0], 0, "h", 0, 1);
assert_token(&tokens[1], 0, "hε", 0, 3);
assert_token(&tokens[2], 0, "ε", 1, 3);
assert_token(&tokens[3], 0, "εl", 1, 4);
assert_token(&tokens[4], 0, "l", 3, 4);
assert_token(&tokens[5], 0, "ll", 3, 5);
assert_token(&tokens[6], 0, "l", 4, 5);
assert_token(&tokens[7], 0, "lo", 4, 6);
assert_token(&tokens[8], 0, "o", 5, 6);
assert_token(&tokens[2], 1, "ε", 1, 3);
assert_token(&tokens[3], 1, "εl", 1, 4);
assert_token(&tokens[4], 2, "l", 3, 4);
assert_token(&tokens[5], 2, "ll", 3, 5);
assert_token(&tokens[6], 3, "l", 4, 5);
assert_token(&tokens[7], 3, "lo", 4, 6);
assert_token(&tokens[8], 4, "o", 5, 6);
}

#[test]
Expand Down Expand Up @@ -470,23 +477,23 @@ mod tests {
#[test]
fn test_stutterring_iterator() {
let mut it = StutteringIterator::new(0..10, 1, 2);
assert_eq!(it.next(), Some((0, 1)));
assert_eq!(it.next(), Some((0, 2)));
assert_eq!(it.next(), Some((1, 2)));
assert_eq!(it.next(), Some((1, 3)));
assert_eq!(it.next(), Some((2, 3)));
assert_eq!(it.next(), Some((2, 4)));
assert_eq!(it.next(), Some((3, 4)));
assert_eq!(it.next(), Some((3, 5)));
assert_eq!(it.next(), Some((4, 5)));
assert_eq!(it.next(), Some((4, 6)));
assert_eq!(it.next(), Some((5, 6)));
assert_eq!(it.next(), Some((5, 7)));
assert_eq!(it.next(), Some((6, 7)));
assert_eq!(it.next(), Some((6, 8)));
assert_eq!(it.next(), Some((7, 8)));
assert_eq!(it.next(), Some((7, 9)));
assert_eq!(it.next(), Some((8, 9)));
assert_eq!(it.next(), Some((0, 0, 1)));
assert_eq!(it.next(), Some((0, 0, 2)));
assert_eq!(it.next(), Some((1, 1, 2)));
assert_eq!(it.next(), Some((1, 1, 3)));
assert_eq!(it.next(), Some((2, 2, 3)));
assert_eq!(it.next(), Some((2, 2, 4)));
assert_eq!(it.next(), Some((3, 3, 4)));
assert_eq!(it.next(), Some((3, 3, 5)));
assert_eq!(it.next(), Some((4, 4, 5)));
assert_eq!(it.next(), Some((4, 4, 6)));
assert_eq!(it.next(), Some((5, 5, 6)));
assert_eq!(it.next(), Some((5, 5, 7)));
assert_eq!(it.next(), Some((6, 6, 7)));
assert_eq!(it.next(), Some((6, 6, 8)));
assert_eq!(it.next(), Some((7, 7, 8)));
assert_eq!(it.next(), Some((7, 7, 9)));
assert_eq!(it.next(), Some((8, 8, 9)));
assert_eq!(it.next(), None);
}
}
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