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error_model.py
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error_model.py
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# Copyright 2017 Neural Networks and Deep Learning lab, MIPT
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import csv
import itertools
from collections import defaultdict, Counter
from heapq import heappop, heappushpop, heappush
from logging import getLogger
from math import log, exp
from typing import List, Iterable, Tuple
from tqdm import tqdm
from deeppavlov.core.common.errors import ConfigError
from deeppavlov.core.common.registry import register
from deeppavlov.core.models.estimator import Estimator
from deeppavlov.vocabs.typos import StaticDictionary
logger = getLogger(__name__)
@register('spelling_error_model')
class ErrorModel(Estimator):
"""Component that uses statistics based error model to find best candidates in a static dictionary.
Based on An Improved Error Model for Noisy Channel Spelling Correction by Eric Brill and Robert C. Moore
Args:
dictionary: a :class:`~deeppavlov.vocabs.typos.StaticDictionary` object
window: maximum context window size
candidates_count: maximum number of replacement candidates to return for every token in the input
Attributes:
costs: logarithmic probabilities of character sequences replacements
dictionary: a :class:`~deeppavlov.vocabs.typos.StaticDictionary` object
window: maximum context window size
candidates_count: maximum number of replacement candidates to return for every token in the input
"""
def __init__(self, dictionary: StaticDictionary, window: int = 1, candidates_count: int = 1, *args, **kwargs):
super().__init__(*args, **kwargs)
self.costs = defaultdict(itertools.repeat(float('-inf')).__next__)
self.dictionary = dictionary
self.window = window
if self.window == 0:
self.find_candidates = self._find_candidates_window_0
else:
self.find_candidates = self._find_candidates_window_n
self.costs[('', '')] = log(1)
self.costs[('⟬', '⟬')] = log(1)
self.costs[('⟭', '⟭')] = log(1)
for c in self.dictionary.alphabet:
self.costs[(c, c)] = log(1)
# if self.ser_path.is_file():
self.load()
self.candidates_count = candidates_count
def _find_candidates_window_0(self, word, prop_threshold=1e-6):
threshold = log(prop_threshold)
d = {}
prefixes_heap = [(0, {''})]
candidates = [(float('-inf'), '') for _ in range(self.candidates_count)]
word = '⟬{}⟭'.format(word.lower().replace('ё', 'е'))
word_len = len(word) + 1
while prefixes_heap and -prefixes_heap[0][0] > candidates[0][0]:
_, prefixes = heappop(prefixes_heap)
for prefix in prefixes:
res = []
for i in range(word_len):
c = word[i - 1:i]
res.append(max(
(res[-1] + self.costs[('', c)]) if i else float('-inf'),
d[prefix[:-1]][i] + self.costs[(prefix[-1], '')] if prefix else float(
'-inf'),
(d[prefix[:-1]][i - 1] + (self.costs[(prefix[-1], c)]))
if prefix and i else float('-inf')
) if i or prefix else 0)
d[prefix] = res
if prefix in self.dictionary.words_set:
heappushpop(candidates, (res[-1], prefix))
potential = max(res)
if potential > threshold:
heappush(prefixes_heap, (-potential, self.dictionary.words_trie[prefix]))
return [(w.strip('⟬⟭'), score) for score, w in sorted(candidates, reverse=True) if
score > threshold]
def _find_candidates_window_n(self, word, prop_threshold=1e-6):
threshold = log(prop_threshold)
word = '⟬{}⟭'.format(word.lower().replace('ё', 'е'))
word_len = len(word) + 1
inf = float('-inf')
d = defaultdict(list)
d[''] = [0.] + [inf] * (word_len - 1)
prefixes_heap = [(0, self.dictionary.words_trie[''])]
candidates = [(inf, '')] * self.candidates_count
while prefixes_heap and -prefixes_heap[0][0] > candidates[0][0]:
_, prefixes = heappop(prefixes_heap)
for prefix in prefixes:
prefix_len = len(prefix)
d[prefix] = res = [inf]
for i in range(1, word_len):
c_res = [inf]
for li in range(1, min(prefix_len + 1, self.window + 2)):
for ri in range(1, min(i + 1, self.window + 2)):
prev = d[prefix[:-li]][i - ri]
if prev > threshold:
edit = (prefix[-li:], word[i - ri:i])
if edit in self.costs:
c_res.append(prev +
self.costs[edit])
res.append(max(c_res))
if prefix in self.dictionary.words_set:
heappushpop(candidates, (res[-1], prefix))
potential = max(res)
# potential = max(
# [e for i in range(self.window + 2) for e in d[prefix[:prefix_len - i]]])
if potential > threshold:
heappush(prefixes_heap, (-potential, self.dictionary.words_trie[prefix]))
return [(w.strip('⟬⟭'), score) for score, w in sorted(candidates, reverse=True) if
score > threshold]
def _infer_instance(self, instance: List[str]) -> List[List[Tuple[float, str]]]:
candidates = []
for incorrect in instance:
if any([c not in self.dictionary.alphabet for c in incorrect]):
candidates.append([(0, incorrect)])
else:
res = self.find_candidates(incorrect, prop_threshold=1e-6)
if res:
candidates.append([(score, candidate) for candidate, score in res])
else:
candidates.append([(0, incorrect)])
return candidates
def __call__(self, data: Iterable[Iterable[str]], *args, **kwargs) -> List[List[List[Tuple[float, str]]]]:
"""Propose candidates for tokens in sentences
Args:
data: batch of tokenized sentences
Returns:
batch of lists of probabilities and candidates for every token
"""
data = list(data)
if len(data) > 1:
data = tqdm(data, desc='Infering a batch with the error model', leave=False)
return [self._infer_instance(instance) for instance in data]
@staticmethod
def _distance_edits(seq1, seq2):
l1, l2 = len(seq1), len(seq2)
d = [[(i, ()) for i in range(l2 + 1)]]
d += [[(i, ())] + [(0, ())] * l2 for i in range(1, l1 + 1)]
for i in range(1, l1 + 1):
for j in range(1, l2 + 1):
edits = [
(d[i - 1][j][0] + 1, d[i - 1][j][1] + ((seq1[i - 1], ''),)),
(d[i][j - 1][0] + 1, d[i][j - 1][1] + (('', seq2[j - 1]),)),
(d[i - 1][j - 1][0] + (seq1[i - 1] != seq2[j - 1]),
d[i - 1][j - 1][1] + ((seq1[i - 1], seq2[j - 1]),))
]
if i > 1 and j > 1 and seq1[i - 1] == seq2[j - 2] and seq1[i - 2] == seq2[j - 1]:
edits.append((d[i - 2][j - 2][0] + (seq1[i - 1] != seq2[j - 1]),
d[i - 2][j - 2][1] + ((seq1[i - 2:i], seq2[j - 2:j]),)))
d[i][j] = min(edits, key=lambda x: x[0])
return d[-1][-1]
def fit(self, x: List[str], y: List[str]):
"""Calculate character sequences replacements probabilities
Args:
x: words with spelling errors
y: words without spelling errors
"""
changes = []
entries = []
data = list(zip(x, y))
window = 4
for error, correct in tqdm(data, desc='Training the error model'):
correct = '⟬{}⟭'.format(' '.join(correct))
error = '⟬{}⟭'.format(' '.join(error))
d, ops = self._distance_edits(correct, error)
if d <= 2:
w_ops = set()
for pos in range(len(ops)):
left, right = list(zip(*ops))
for l in range(pos, max(0, pos - window) - 1, -1):
for r in range(pos + 1, min(len(ops), l + 2 + window)):
w_ops.add(((''.join(left[l:r]), ''.join(right[l:r])), l, r))
ops = [x[0] for x in w_ops]
entries += [op[0] for op in ops]
changes += [op for op in ops]
e_count = Counter(entries)
c_count = Counter(changes)
incorrect_prior = 1
correct_prior = 19
for (w, s), c in c_count.items():
c = c + (incorrect_prior if w != s else correct_prior)
e = e_count[w] + incorrect_prior + correct_prior
p = c / e
self.costs[(w, s)] = log(p)
def save(self):
"""Save replacements probabilities to a file
"""
logger.info("[saving error_model to `{}`]".format(self.save_path))
with open(self.save_path, 'w', newline='', encoding='utf8') as tsv_file:
writer = csv.writer(tsv_file, delimiter='\t')
for (w, s), log_p in self.costs.items():
writer.writerow([w, s, exp(log_p)])
def load(self):
"""Load replacements probabilities from a file
"""
if self.load_path:
if self.load_path.is_file():
logger.debug("loading error_model from `{}`".format(self.load_path))
with open(self.load_path, 'r', newline='', encoding='utf8') as tsv_file:
reader = csv.reader(tsv_file, delimiter='\t')
for w, s, p in reader:
self.costs[(w, s)] = log(float(p))
elif not self.load_path.parent.is_dir():
raise ConfigError("Provided `load_path` for {} doesn't exist!".format(
self.__class__.__name__))
else:
logger.warning('No load_path provided, initializing error model from scratch')