R语言2行代码实现
sorted_words<-names(sort(table(strsplit(tolower(paste(readLines("http://www.norvig.com/big.txt"),collapse=" ")),"[^a-z]+")),decreasing=TRUE))
correct<-function(word){c(sorted_words[adist(word,sorted_words)<=min(adist(word,sorted_words),2)],word)[1]}
代码解释
# Read in big.txt, a 6.5 mb collection of different English texts.
raw_text<-paste(readLines("http://www.norvig.com/big.txt"),collapse=" ")
# Make the text lowercase and split it up creating a huge vector of word tokens.
split_text<-strsplit(tolower(raw_text),"[^a-z]+")
# Count the number of different type of words.
word_count<-table(split_text)
# Sort the words and create an ordered vector with the most common type of words first.
sorted_words<-names(sort(word_count,decreasing=TRUE))
correct<-function(word)
# Calculate the edit distance between the word and all other words in sorted_words.
edit_dist<-adist(word,sorted_words)
# Calculate the minimum edit distance to find a word that exists in big.txt
# with a limit of two edits.
min_edit_dist<-min(edit_dist,2)
# Generate a vector with all words with this minimum edit distance.
# Since sorted_words is ordered from most common to least common, the resulting
# vector will have the most common / probable match first.
proposals_by_prob<-c(sorted_words[edit_dist<=min(edit_dist,2)])
# In case proposals_by_prob would be empty we append the word to be corrected...
proposals_by_prob<-c(proposals_by_prob,word)
# ... and return the first / most probable word in the vector.
proposals_by_prob[1]
Python 21行代码实现
"""Spelling Corrector in Python 3; see http://norvig.com/spell-correct.html
Copyright (c) 2007-2016 Peter Norvig
MIT license: www.opensource.org/licenses/mit-license.php
"""
################ Spelling Corrector
import re
from collections import Counter
def words(text): return re.findall(r'\w+', text.lower())
WORDS = Counter(words(open('big.txt').read()))
def P(word, N=sum(WORDS.values())):
"Probability of `word`."
return WORDS[word] / N
def correction(word):
"Most probable spelling correction for word."
return max(candidates(word), key=P)
def candidates(word):
"Generate possible spelling corrections for word."
return (known([word]) or known(edits1(word)) or known(edits2(word)) or [word])
def known(words):
"The subset of `words` that appear in the dictionary of WORDS."
return set(w for w in words if w in WORDS)
def edits1(word):
"All edits that are one edit away from `word`."
letters = 'abcdefghijklmnopqrstuvwxyz'
splits = [(word[:i], word[i:]) for i in range(len(word) + 1)]
deletes = [L + R[1:] for L, R in splits if R]
transposes = [L + R[1] + R[0] + R[2:] for L, R in splits if len(R)>1]
replaces = [L + c + R[1:] for L, R in splits if R for c in letters]
inserts = [L + c + R for L, R in splits for c in letters]
return set(deletes + transposes + replaces + inserts)
def edits2(word):
"All edits that are two edits away from `word`."
return (e2 for e1 in edits1(word) for e2 in edits1(e1))
测试代码
################ Test Code
def unit_tests():
assert correction('speling') == 'spelling' # insert
assert correction('korrectud') == 'corrected' # replace 2
assert correction('bycycle') == 'bicycle' # replace
assert correction('inconvient') == 'inconvenient' # insert 2
assert correction('arrainged') == 'arranged' # delete
assert correction('peotry') =='poetry' # transpose
assert correction('peotryy') =='poetry' # transpose + delete
assert correction('word') == 'word' # known
assert correction('quintessential') == 'quintessential' # unknown
assert words('This is a TEST.') == ['this', 'is', 'a', 'test']
assert Counter(words('This is a test. 123; A TEST this is.')) == (
Counter({'123': 1, 'a': 2, 'is': 2, 'test': 2, 'this': 2}))
assert len(WORDS) == 32192
assert sum(WORDS.values()) == 1115504
assert WORDS.most_common(10) == [
('the', 79808),
('of', 40024),
('and', 38311),
('to', 28765),
('in', 22020),
('a', 21124),
('that', 12512),
('he', 12401),
('was', 11410),
('it', 10681)]
assert WORDS['the'] == 79808
assert P('quintessential') == 0
assert 0.07 < P('the') < 0.08
return 'unit_tests pass'
def spelltest(tests, verbose=False):
"Run correction(wrong) on all (right, wrong) pairs; report results."
import time
start = time.clock()
good, unknown = 0, 0
n = len(tests)
for right, wrong in tests:
w = correction(wrong)
good += (w == right)
if w != right:
unknown += (right not in WORDS)
if verbose:
print('correction({}) => {} ({}); expected {} ({})'
.format(wrong, w, WORDS[w], right, WORDS[right]))
dt = time.clock() - start
print('{:.0%} of {} correct ({:.0%} unknown) at {:.0f} words per second '
.format(good / n, n, unknown / n, n / dt))
def Testset(lines):
"Parse 'right: wrong1 wrong2' lines into [('right', 'wrong1'), ('right', 'wrong2')] pairs."
return [(right, wrong)
for (right, wrongs) in (line.split(':') for line in lines)
for wrong in wrongs.split()]
if __name__ == '__main__':
print(unit_tests())
spelltest(Testset(open('spell-testset1.txt')))
spelltest(Testset(open('spell-testset2.txt')))
致谢：
- norvig大大 http://norvig.com/spell-correct.html