NLP(04)_英文文本处理与spaCy

英文文本处理与spaCy

spaCy是Python和Cython中的高级自然语言处理库，它建立在最新的研究基础之上，从一开始就设计用于实际产品。spaCy 带有预先训练的统计模型和单词向量，目前支持 20 多种语言的标记。它具有世界上速度最快的句法分析器，用于标签的卷积神经网络模型，解析和命名实体识别以及与深度学习整合。

0.英文Tokenization(标记化/分词)

文本是不能成段送入模型中进行分析的，我们通常会把文本切成有独立含义的字、词或者短语，这个过程叫做tokenization，这通常是大家解决自然语言处理问题的第一步。在spaCY中同样可以很方便地完成Tokenization。

import spacy
nlp = spacy.load('en')
doc = nlp('Hello World! My name is HanXiaoyang')
for token in doc:
    print('"' + token.text + '"')
    
->"Hello"
"World"
"!"
"My"
"name"
"is"
"HanXiaoyang"

每个token对象有着非常丰富的属性，如下的方式可以取出其中的部分属性。

doc = nlp("Next week I'll   be in Shanghai.")
for token in doc:
    print("{0}\t{1}\t{2}\t{3}\t{4}\t{5}\t{6}\t{7}".format(
        token.text,
        token.idx,
        token.lemma_,
        token.is_punct,
        token.is_space,
        token.shape_,
        token.pos_,
        token.tag_
    ))
    
->  Next	0	next	False	False	Xxxx	ADJ	JJ
    week	5	week	False	False	xxxx	NOUN	NN
    I	10	-PRON-	False	False	X	PRON	PRP
    'll	11	will	False	False	'xx	VERB	MD
      	15	  	False	True	  	SPACE	_SP
    be	17	be	False	False	xx	VERB	VB
    in	20	in	False	False	xx	ADP	IN
    Shanghai	23	shanghai	False	False	Xxxxx	PROPN	NNP
    .	31	.	True	False	.	PUNCT	

.
断句功能在spaCy中也有体现，如下

# 断句
doc = nlp("Hello World! My name is HanXiaoyang")
for sent in doc.sents:
    print(sent)
    
->Hello World!
  My name is HanXiaoyang

1.词性标注

词性（part-of-speech）是词汇基本的语法属性，通常也称为词性。

词性标注（part-of-speech tagging）,又称为词类标注或者简称标注，是指为分词结果中的每个单词标注一个正确的词性的程序，也即确定每个词是名词、动词、形容词或者其他词性的过程。

词性标注是很多NLP任务的预处理步骤，如句法分析，经过词性标注后的文本会带来很大的便利性，但也不是不可或缺的步骤。
词性标注的最简单做法是选取最高频词性，主流的做法可以分为基于规则和基于统计的方法，包括：

• 基于最大熵的词性标注
• 基于统计最大概率输出词性
• 基于HMM的词性标注

# 词性标注
doc = nlp("Next week I'll be in Shanghai.")
print([(token.text, token.tag_) for token in doc])

->[('Next', 'JJ'), ('week', 'NN'), ('I', 'PRP'), ("'ll", 'MD'), ('be', 'VB'), ('in', 'IN'), ('Shanghai', 'NNP'), ('.', '.')]

具体的词性标注编码和含义见如下对应表：

POS Tag	Description	Example
CC	coordinating conjunction	and
CD	cardinal number	1, third
DT	determiner	the
EX	existential there	there, is
FW	foreign word	d’hoevre
IN	preposition or subordinating conjunction	in, of, like
JJ	adjective	big
JJR	adjective, comparative	bigger
JJS	adjective, superlative	biggest
LS	list marker	1)
MD	modal	could, will
NN	noun, singular or mass	door
NNS	noun plural	doors
NNP	proper noun, singular	John
NNPS	proper noun, plural	Vikings
PDT	predeterminer	both the boys
POS	possessive ending	friend‘s
PRP	personal pronoun	I, he, it
PRP$	possessive pronoun	my, his
RB	adverb	however, usually, naturally, here, good
RBR	adverb, comparative	better
RBS	adverb, superlative	best
RP	particle	give up
TO	to	to go, to him
UH	interjection	uhhuhhuhh
VB	verb, base form	take
VBD	verb, past tense	took
VBG	verb, gerund or present participle	taking
VBN	verb, past participle	taken
VBP	verb, sing. present, non-3d	take
VBZ	verb, 3rd person sing. present	takes
WDT	wh-determiner	which
WP	wh-pronoun	who, what
WP$	possessive wh-pronoun	whose
WRB	wh-abverb	where, when

2.命名实体识别

命名实体识别（Named Entity Recognition，简称NER），又称作“专名识别”，是指识别文本中具有特定意义的实体，主要包括人名、地名、机构名、专有名词等。通常包括两部分：1) 实体边界识别；2) 确定实体类别（人名、地名、机构名或其他）。

doc = nlp("Next week I'll be in Shanghai.")
for ent in doc.ents:
    print(ent.text, ent.label_)
    
>>Next week DATE
  Shanghai GPE

from nltk.chunk import conlltags2tree

doc = nlp("Next week I'll be in Shanghai.")
iob_tagged = [
    (
        token.text, 
        token.tag_, 
        "{0}-{1}".format(token.ent_iob_, token.ent_type_) if token.ent_iob_ != 'O' else token.ent_iob_
    ) for token in doc
]
 
print(iob_tagged)
# 按照nltk.Tree的格式显示
print(conlltags2tree(iob_tagged))

>>[('Next', 'JJ', 'B-DATE'), ('week', 'NN', 'I-DATE'), ('I', 'PRP', 'O'), ("'ll", 'MD', 'O'), ('be', 'VB', 'O'), ('in', 'IN', 'O'), ('Shanghai', 'NNP', 'B-GPE'), ('.', '.', 'O')]
(S
  (DATE Next/JJ week/NN)
  I/PRP
  'll/MD
  be/VB
  in/IN
  (GPE Shanghai/NNP)
  ./.)

spaCy中包含的命名实体非常丰富，如下例所示：

doc = nlp("I just bought 2 shares at 9 a.m. because the stock went up 30% in just 2 days according to the WSJ")
for ent in doc.ents:
    print(ent.text, ent.label_)
>>2 CARDINAL
  9 a.m. TIME
  30% PERCENT
  just 2 days DATE
  WSJ ORG

还可以用非常漂亮的可视化做显示：

from spacy import displacy
 
doc = nlp('I just bought 2 shares at 9 a.m. because the stock went up 30% in just 2 days according to the WSJ')
displacy.render(doc, style='ent', jupyter=True)

3.chunking/组块分析

spaCy可以自动检测名词短语，并输出根(root)词，比如下面的"Journal",“piece”,“currencies”

doc = nlp("Wall Street Journal just published an interesting piece on crypto currencies")
for chunk in doc.noun_chunks:
    print(chunk.text, chunk.label_, chunk.root.text)
    
>>Wall Street Journal NP Journal
  an interesting piece NP piece
  crypto currencies NP currencies

4.句法依存解析

spaCy有着非常强大的句法依存解析功能，可以试试对句子进行解析。

doc = nlp('Wall Street Journal just published an interesting piece on crypto currencies')
 
for token in doc:
    print("{0}/{1} <--{2}-- {3}/{4}".format(
        token.text, token.tag_, token.dep_, token.head.text, token.head.tag_))
        
 >>Wall/NNP <--compound-- Street/NNP
  Street/NNP <--compound-- Journal/NNP
  Journal/NNP <--nsubj-- published/VBD
  just/RB <--advmod-- published/VBD
  published/VBD <--ROOT-- published/VBD
  an/DT <--det-- piece/NN
  interesting/JJ <--amod-- piece/NN
  piece/NN <--dobj-- published/VBD
  on/IN <--prep-- piece/NN
  crypto/JJ <--compound-- currencies/NNS
  currencies/NNS <--pobj-- on/IN

from spacy import displacy
 
doc = nlp('Wall Street Journal just published an interesting piece on crypto currencies')
displacy.render(doc, style='dep', jupyter=True, options={'distance': 90})

>>Wall PROPN Street PROPN Journal PROPN just ADV published VERB an DET interesting ADJ piece NOUN on ADP crypto ADJ currencies NOUN compound compound nsubj advmod det amod dobj prep compound pobj

5.词向量使用

NLP中有一个非常强大的文本表示学习方法叫做word2vec，通过词的上下文学习到词语的稠密向量化表示，同时在这个表示形态下，语义相关的词在向量空间中会比较接近。也有类似v(爷爷)-v(奶奶) ≈ v(男人)-v(女人)的关系。

如果大家要使用英文的词向量，需要先下载预先训练好的结果。

命令：python3 -m spacy download en_core_web_lg

nlp = spacy.load('en_core_web_lg')
print(nlp.vocab['banana'].vector[0:10])

>>[ 0.20228  -0.076618  0.37032   0.032845 -0.41957   0.072069 -0.37476
  0.05746  -0.012401  0.52949 ]

from scipy import spatial

# 余弦相似度计算
cosine_similarity = lambda x, y: 1 - spatial.distance.cosine(x, y)

# 男人、女人、国王、女王 的词向量
man = nlp.vocab['man'].vector
woman = nlp.vocab['woman'].vector
queen = nlp.vocab['queen'].vector
king = nlp.vocab['king'].vector
 
# 我们对向量做一个简单的计算，"man" - "woman" + "queen"
maybe_king = man - woman + queen
computed_similarities = []

# 扫描整个词库的词向量做比对，召回最接近的词向量
for word in nlp.vocab:
    if not word.has_vector:
        continue
 
    similarity = cosine_similarity(maybe_king, word.vector)
    computed_similarities.append((word, similarity))

# 排序与最接近结果展示
computed_similarities = sorted(computed_similarities, key=lambda item: -item[1])
print([w[0].text for w in computed_similarities[:10]])

>>['Queen', 'QUEEN', 'queen', 'King', 'KING', 'king', 'KIng', 'Kings', 'KINGS', 'kings']

6.词汇与文本相似度

在词向量的基础上，spaCy提供了从词到文档的相似度计算的方法，下面的例子是它的使用方法。

# 词汇语义相似度(关联性)
banana = nlp.vocab['banana']
dog = nlp.vocab['dog']
fruit = nlp.vocab['fruit']
animal = nlp.vocab['animal']
 
print(dog.similarity(animal), dog.similarity(fruit)) # 0.6618534 0.23552845
print(banana.similarity(fruit), banana.similarity(animal)) # 0.67148364 0.2427285

# 文本语义相似度(关联性)
target = nlp("Cats are beautiful animals.")
 
doc1 = nlp("Dogs are awesome.")
doc2 = nlp("Some gorgeous creatures are felines.")
doc3 = nlp("Dolphins are swimming mammals.")
 
print(target.similarity(doc1))  # 0.8901765218466683
print(target.similarity(doc2))  # 0.9115828449161616
print(target.similarity(doc3))  # 0.7822956752876101