我想在 python 中使用 wordnet lemmatizer，并且我了解到默认的 pos 标记是 NOUN，并且它不会为动词输出正确的 lemma，除非 pos 标记明确指定为 VERB。
我的问题是，为了准确地执行上述词形还原，最好的方法是什么？
我使用了 pos 标记，nltk.pos_tag并且在将树库 pos 标签集成到 wordnet 兼容的 pos 标签时迷失了方向。请帮忙
from nltk.stem.wordnet import WordNetLemmatizer
lmtzr = WordNetLemmatizer()
tagged = nltk.pos_tag(tokens)
我得到了 NN、JJ、VB、RB 中的输出标签。如何将这些更改为与 wordnet 兼容的标签？
我还必须nltk.pos_tag()使用标记的语料库进行训练，还是可以直接在我的数据上使用它来评估？
首先，您nltk.pos_tag()无需培训即可直接使用。该函数将从文件中加载预训练的标记器。您可以使用以下命令查看文件名nltk.tag._POS_TAGGER：
nltk.tag._POS_TAGGER
>>> 'taggers/maxent_treebank_pos_tagger/english.pickle'
由于它是使用 Treebank 语料库训练的，因此它也使用Treebank 标签集。
以下函数将树库标签映射到 WordNet 词性名称：
from nltk.corpus import wordnet
def get_wordnet_pos(treebank_tag):
if treebank_tag.startswith('J'):
return wordnet.ADJ
elif treebank_tag.startswith('V'):
return wordnet.VERB
elif treebank_tag.startswith('N'):
return wordnet.NOUN
elif treebank_tag.startswith('R'):
return wordnet.ADV
else:
return ''
然后，您可以将返回值与 lemmatizer 一起使用：
from nltk.stem.wordnet import WordNetLemmatizer
lemmatizer = WordNetLemmatizer()
lemmatizer.lemmatize('going', wordnet.VERB)
>>> 'go'
在将返回值传递给 Lemmatizer 之前检查返回值，因为空字符串会给出KeyError.
如 nltk.corpus.reader.wordnet 的源代码（http://www.nltk.org/_modules/nltk/corpus/reader/wordnet.html）
#{ Part-of-speech constants
ADJ, ADJ_SAT, ADV, NOUN, VERB = 'a', 's', 'r', 'n', 'v'
#}
POS_LIST = [NOUN, VERB, ADJ, ADV]
转换步骤：Document->Sentences->Tokens->POS->Lemmas
import nltk
from nltk.stem import WordNetLemmatizer
from nltk.corpus import wordnet
#example text text = 'What can I say about this place. The staff of these restaurants is nice and the eggplant is not bad'
class Splitter(object):
"""
split the document into sentences and tokenize each sentence
"""
def __init__(self):
self.splitter = nltk.data.load('tokenizers/punkt/english.pickle')
self.tokenizer = nltk.tokenize.TreebankWordTokenizer()
def split(self,text):
"""
out : ['What', 'can', 'I', 'say', 'about', 'this', 'place', '.']
"""
# split into single sentence
sentences = self.splitter.tokenize(text)
# tokenization in each sentences
tokens = [self.tokenizer.tokenize(sent) for sent in sentences]
return tokens
class LemmatizationWithPOSTagger(object):
def __init__(self):
pass
def get_wordnet_pos(self,treebank_tag):
"""
return WORDNET POS compliance to WORDENT lemmatization (a,n,r,v)
"""
if treebank_tag.startswith('J'):
return wordnet.ADJ
elif treebank_tag.startswith('V'):
return wordnet.VERB
elif treebank_tag.startswith('N'):
return wordnet.NOUN
elif treebank_tag.startswith('R'):
return wordnet.ADV
else:
# As default pos in lemmatization is Noun
return wordnet.NOUN
def pos_tag(self,tokens):
# find the pos tagginf for each tokens [('What', 'WP'), ('can', 'MD'), ('I', 'PRP') ....
pos_tokens = [nltk.pos_tag(token) for token in tokens]
# lemmatization using pos tagg
# convert into feature set of [('What', 'What', ['WP']), ('can', 'can', ['MD']), ... ie [original WORD, Lemmatized word, POS tag]
pos_tokens = [ [(word, lemmatizer.lemmatize(word,self.get_wordnet_pos(pos_tag)), [pos_tag]) for (word,pos_tag) in pos] for pos in pos_tokens]
return pos_tokens
lemmatizer = WordNetLemmatizer()
splitter = Splitter()
lemmatization_using_pos_tagger = LemmatizationWithPOSTagger()
#step 1 split document into sentence followed by tokenization
tokens = splitter.split(text)
#step 2 lemmatization using pos tagger
lemma_pos_token = lemmatization_using_pos_tagger.pos_tag(tokens)
print(lemma_pos_token)
您可以使用 python 默认字典创建地图，并利用以下事实：对于词形还原器，默认标签是名词。
from nltk.corpus import wordnet as wn
from nltk.stem.wordnet import WordNetLemmatizer
from nltk import word_tokenize, pos_tag
from collections import defaultdict
tag_map = defaultdict(lambda : wn.NOUN)
tag_map['J'] = wn.ADJ
tag_map['V'] = wn.VERB
tag_map['R'] = wn.ADV
text = "Another way of achieving this task"
tokens = word_tokenize(text)
lmtzr = WordNetLemmatizer()
for token, tag in pos_tag(tokens):
lemma = lmtzr.lemmatize(token, tag_map[tag[0]])
print(token, "=>", lemma)
@Suzana_K 正在工作。但是我有一些情况导致 KeyError 作为@Clock Slave 提到的。
将树库标签转换为 Wordnet 标签
from nltk.corpus import wordnet
def get_wordnet_pos(treebank_tag):
if treebank_tag.startswith('J'):
return wordnet.ADJ
elif treebank_tag.startswith('V'):
return wordnet.VERB
elif treebank_tag.startswith('N'):
return wordnet.NOUN
elif treebank_tag.startswith('R'):
return wordnet.ADV
else:
return None # for easy if-statement
现在，只有当我们有 wordnet 标签时，我们才将 pos 输入到 lemmatize 函数中
from nltk.stem.wordnet import WordNetLemmatizer
lemmatizer = WordNetLemmatizer()
tagged = nltk.pos_tag(tokens)
for word, tag in tagged:
wntag = get_wordnet_pos(tag)
if wntag is None:# not supply tag in case of None
lemma = lemmatizer.lemmatize(word)
else:
lemma = lemmatizer.lemmatize(word, pos=wntag)
您可以执行以下操作：
import nltk
from nltk.corpus import wordnet
wordnet_map = {
"N": wordnet.NOUN,
"V": wordnet.VERB,
"J": wordnet.ADJ,
"R": wordnet.ADV
}
def pos_tag_wordnet(text):
"""
Create pos_tag with wordnet format
"""
pos_tagged_text = nltk.pos_tag(text)
# map the pos tagging output with wordnet output
pos_tagged_text = [
(word, wordnet_map.get(pos_tag[0])) if pos_tag[0] in wordnet_map.keys()
else (word, wordnet.NOUN)
for (word, pos_tag) in pos_tagged_text
]
return pos_tagged_text
您可以在一行中执行此操作：
wnpos = lambda e: ('a' if e[0].lower() == 'j' else e[0].lower()) if e[0].lower() in ['n', 'r', 'v'] else 'n'
然后用于wnpos(nltk_pos)获取 POS 给 .lemmatize()。在你的情况下，lmtzr.lemmatize(word=tagged[0][0], pos=wnpos(tagged[0][1])).
在网上搜索后，我找到了这个解决方案：从句子到“词袋”经过拆分、pos_tagging、词形还原和清理（从标点符号和“停止词”）操作得出。这是我的代码：
from nltk.corpus import wordnet as wn
from nltk.wsd import lesk
from nltk.stem import WordNetLemmatizer
from nltk.corpus import stopwords
from nltk.tokenize import word_tokenize
punctuation = u",.?!()-_\"\'\\\n\r\t;:+*<>@#§^$%&|/"
stop_words_eng = set(stopwords.words('english'))
lemmatizer = WordNetLemmatizer()
tag_dict = {"J": wn.ADJ,
"N": wn.NOUN,
"V": wn.VERB,
"R": wn.ADV}
def extract_wnpostag_from_postag(tag):
#take the first letter of the tag
#the second parameter is an "optional" in case of missing key in the dictionary
return tag_dict.get(tag[0].upper(), None)
def lemmatize_tupla_word_postag(tupla):
"""
giving a tupla of the form (wordString, posTagString) like ('guitar', 'NN'), return the lemmatized word
"""
tag = extract_wnpostag_from_postag(tupla[1])
return lemmatizer.lemmatize(tupla[0], tag) if tag is not None else tupla[0]
def bag_of_words(sentence, stop_words=None):
if stop_words is None:
stop_words = stop_words_eng
original_words = word_tokenize(sentence)
tagged_words = nltk.pos_tag(original_words) #returns a list of tuples: (word, tagString) like ('And', 'CC')
original_words = None
lemmatized_words = [ lemmatize_tupla_word_postag(ow) for ow in tagged_words ]
tagged_words = None
cleaned_words = [ w for w in lemmatized_words if (w not in punctuation) and (w not in stop_words) ]
lemmatized_words = None
return cleaned_words
sentence = "Two electric guitar rocks players, and also a better bass player, are standing off to two sides reading corpora while walking"
print(sentence, "\n\n bag of words:\n", bag_of_words(sentence) )