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use std::ops::{Index, Range};
use std::str;
use ahash::AHashMap as HashMap;
use smartstring::alias::String;
#[cfg(feature = "__test_data")]
pub mod test_data;
pub struct Segmenter {
unigrams: HashMap<String, f64>,
bigrams: HashMap<(String, String), f64>,
total: f64,
limit: usize,
}
impl Segmenter {
pub fn from_iters<U, B>(unigrams: U, bigrams: B) -> Self
where
U: Iterator<Item = (String, f64)>,
B: Iterator<Item = ((String, String), f64)>,
{
Self {
unigrams: unigrams.collect::<HashMap<_, _>>(),
bigrams: bigrams.collect::<HashMap<_, _>>(),
limit: DEFAULT_LIMIT,
total: DEFAULT_TOTAL,
}
}
pub fn segment(&self, text: &str, out: &mut Vec<String>) {
SegmentState::new(&Ascii::new(text), &self, out).run()
}
fn score(&self, word: &str, previous: Option<&str>) -> f64 {
if let Some(prev) = previous {
if let Some(bi) = self.bigrams.get(&(prev.into(), word.into())) {
if let Some(uni) = self.unigrams.get(prev) {
return (bi / self.total) / (uni / self.total);
}
}
}
match self.unigrams.get(word) {
Some(p) => p / self.total,
None => 10.0 / (self.total * 10.0f64.powf(word.len() as f64)),
}
}
pub fn set_limit(&mut self, limit: usize) {
self.limit = limit;
}
pub fn set_total(&mut self, total: f64) {
self.total = total;
}
}
struct SegmentState<'a> {
data: &'a Segmenter,
text: &'a Ascii,
memo: HashMap<MemoKey, (f64, Range<usize>)>,
split_cache: Vec<usize>,
result: &'a mut Vec<String>,
best: Vec<Vec<usize>>,
}
impl<'a> SegmentState<'a> {
fn new(text: &'a Ascii, data: &'a Segmenter, result: &'a mut Vec<String>) -> Self {
Self {
data,
text,
memo: HashMap::new(),
split_cache: Vec::new(),
result,
best: vec![vec![]; SEGMENT_SIZE],
}
}
fn run(mut self) {
let (mut start, mut end) = (0, 0);
while end < self.text.len() {
end = self.text.len().min(end + SEGMENT_SIZE);
self.search(0, start..end, None);
let mut splits = &self.best[0][..];
if end < self.text.len() {
splits = &splits[..splits.len().saturating_sub(5)];
}
for &split in splits {
self.result.push(self.text[start..split].into());
start = split;
}
}
}
fn search(&mut self, level: usize, range: Range<usize>, previous: Option<Range<usize>>) -> f64 {
if range.is_empty() {
self.best[level].clear();
return 0.0;
}
let mut best = f64::MIN;
for split in 1..(range.len().min(self.data.limit) + 1) {
let (start, split, end) = (range.start, range.start + split, range.end);
let previous = previous.clone().map(|range| &self.text[range]);
let prefix_score = self.data.score(&self.text[start..split], previous).log10();
let pair = (split..end, start..split);
let (suffix_score, suffix_splits) = match self.memo.get(&pair) {
Some((score, splits)) => (*score, &self.split_cache[splits.start..splits.end]),
None => {
let suffix_score = self.search(level + 1, split..end, Some(start..split));
let start = self.split_cache.len();
self.split_cache.extend(&self.best[level + 1][..]);
let end = self.split_cache.len();
self.memo.insert(pair, (suffix_score, start..end));
(suffix_score, &self.split_cache[start..end])
}
};
let score = prefix_score + suffix_score;
if score > best {
best = score;
let splits = &mut self.best[level];
splits.clear();
splits.push(split);
splits.extend(suffix_splits);
}
}
best
}
}
type MemoKey = (Range<usize>, Range<usize>);
struct Ascii(Vec<u8>);
impl Ascii {
fn new(s: &str) -> Self {
Self(
s.chars()
.filter_map(|c| match c.is_ascii_alphanumeric() {
true => Some(c.to_ascii_lowercase()),
false => None,
})
.collect::<std::string::String>()
.into_bytes(),
)
}
fn len(&self) -> usize {
self.0.len()
}
}
impl Index<Range<usize>> for Ascii {
type Output = str;
fn index(&self, index: Range<usize>) -> &Self::Output {
let bytes = self.0.index(index);
unsafe { str::from_utf8_unchecked(bytes) }
}
}
const DEFAULT_LIMIT: usize = 24;
const DEFAULT_TOTAL: f64 = 1_024_908_267_229.0;
const SEGMENT_SIZE: usize = 250;
#[cfg(test)]
pub mod tests {
#[test]
fn test_clean() {
let text = super::Ascii::new("Can't buy me love!");
assert_eq!(&text[0..text.len()], "cantbuymelove");
}
}