你可能想尝试一下cos文档相似度的在线服务http://www.scurtu.it/documentSimilarity.html

import urllib,urllib2
import json
API_URL="http://www.scurtu.it/apis/documentSimilarity"
inputDict={}
inputDict['doc1']='Document with some text'
inputDict['doc2']='Other document with some text'
params = urllib.urlencode(inputDict)    
f = urllib2.urlopen(API_URL, params)
response= f.read()
responseObject=json.loads(response)  
print responseObject

句法相似性 有3种简单的方法来检测相似性。

Word2Vec 手套 Tfidf或countvectorizer

语义相似性 可以使用BERT嵌入和尝试不同的词池策略来获得文档嵌入，然后在文档嵌入上应用余弦相似度。

一种先进的方法是利用BERT分数来获得相似度。

研究论文链接:https://arxiv.org/abs/1904.09675

这是一个老问题了，但我发现斯派西可以很容易地解决这个问题。读取文档后，可以使用简单的api相似性来查找文档向量之间的余弦相似性。

首先安装包并下载模型:

pip install spacy
python -m spacy download en_core_web_sm

然后用like so:

import spacy
nlp = spacy.load('en_core_web_sm')
doc1 = nlp(u'Hello hi there!')
doc2 = nlp(u'Hello hi there!')
doc3 = nlp(u'Hey whatsup?')

print (doc1.similarity(doc2)) # 0.999999954642
print (doc2.similarity(doc3)) # 0.699032527716
print (doc1.similarity(doc3)) # 0.699032527716

如果您对测量两段文本的语义相似性更感兴趣，我建议您看看这个gitlab项目。你可以把它作为服务器运行，也有一个预先构建的模型，你可以很容易地使用它来测量两段文本的相似性;尽管它主要用于测量两个句子的相似度，但你仍然可以在你的情况下使用它。它是用java编写的，但您可以将其作为RESTful服务运行。

另一个选择是DKPro Similarity，这是一个库，有各种算法来测量文本的相似性。然而，它也是用java编写的。

代码示例:

// this similarity measure is defined in the dkpro.similarity.algorithms.lexical-asl package
// you need to add that to your .pom to make that example work
// there are some examples that should work out of the box in dkpro.similarity.example-gpl 
TextSimilarityMeasure measure = new WordNGramJaccardMeasure(3);    // Use word trigrams

String[] tokens1 = "This is a short example text .".split(" ");   
String[] tokens2 = "A short example text could look like that .".split(" ");

double score = measure.getSimilarity(tokens1, tokens2);

System.out.println("Similarity: " + score);

常见的方法是将文档转换为TF-IDF向量，然后计算它们之间的余弦相似度。任何关于信息检索(IR)的教科书都涵盖了这一点。参见《信息检索导论》，该书可在网上免费获得。

两两计算相似度

TF-IDF(以及类似的文本转换)在Python包Gensim和scikit-learn中实现。在后一个包中，计算余弦相似度非常简单

from sklearn.feature_extraction.text import TfidfVectorizer

documents = [open(f).read() for f in text_files]
tfidf = TfidfVectorizer().fit_transform(documents)
# no need to normalize, since Vectorizer will return normalized tf-idf
pairwise_similarity = tfidf * tfidf.T

或者，如果文档是普通字符串，

>>> corpus = ["I'd like an apple", 
...           "An apple a day keeps the doctor away", 
...           "Never compare an apple to an orange", 
...           "I prefer scikit-learn to Orange", 
...           "The scikit-learn docs are Orange and Blue"]                                                                                                                                                                                                   
>>> vect = TfidfVectorizer(min_df=1, stop_words="english")                                                                                                                                                                                                   
>>> tfidf = vect.fit_transform(corpus)                                                                                                                                                                                                                       
>>> pairwise_similarity = tfidf * tfidf.T 

尽管Gensim在这类任务中可能有更多选择。

再看看这个问题。

[免责声明:我参与了scikit-learn TF-IDF的实现。]

解读结果

从上面来看，pairwise_similarity是一个方形的Scipy稀疏矩阵，行数和列数等于语料库中文档的数量。

>>> pairwise_similarity                                                                                                                                                                                                                                      
<5x5 sparse matrix of type '<class 'numpy.float64'>'
    with 17 stored elements in Compressed Sparse Row format>

你可以通过.toarray()或.A将稀疏数组转换为NumPy数组:

>>> pairwise_similarity.toarray()                                                                                                                                                                                                                            
array([[1.        , 0.17668795, 0.27056873, 0.        , 0.        ],
       [0.17668795, 1.        , 0.15439436, 0.        , 0.        ],
       [0.27056873, 0.15439436, 1.        , 0.19635649, 0.16815247],
       [0.        , 0.        , 0.19635649, 1.        , 0.54499756],
       [0.        , 0.        , 0.16815247, 0.54499756, 1.        ]])

假设我们想要找到与最终文档最相似的文档，“the scikit-learn docs are Orange and Blue”。本文语料库索引为4。您可以通过取该行的argmax来找到最相似文档的索引，但首先需要屏蔽1,1表示每个文档与其自身的相似性。你可以通过np.fill_diagonal()来实现后者，通过np.nanargmax()来实现前者:

>>> import numpy as np     
                                                                                                                                                                                                                                  
>>> arr = pairwise_similarity.toarray()     
>>> np.fill_diagonal(arr, np.nan)                                                                                                                                                                                                                            
                                                                                                                                                                                                                 
>>> input_doc = "The scikit-learn docs are Orange and Blue"                                                                                                                                                                                                  
>>> input_idx = corpus.index(input_doc)                                                                                                                                                                                                                      
>>> input_idx                                                                                                                                                                                                                                                
4

>>> result_idx = np.nanargmax(arr[input_idx])                                                                                                                                                                                                                
>>> corpus[result_idx]                                                                                                                                                                                                                                       
'I prefer scikit-learn to Orange'

注意:使用稀疏矩阵的目的是为大型语料库和词汇表节省(大量空间)。你可以这样做，而不是转换为NumPy数组:

>>> n, _ = pairwise_similarity.shape                                                                                                                                                                                                                         
>>> pairwise_similarity[np.arange(n), np.arange(n)] = -1.0
>>> pairwise_similarity[input_idx].argmax()                                                                                                                                                                                                                  
3

Generally a cosine similarity between two documents is used as a similarity measure of documents. In Java, you can use Lucene (if your collection is pretty large) or LingPipe to do this. The basic concept would be to count the terms in every document and calculate the dot product of the term vectors. The libraries do provide several improvements over this general approach, e.g. using inverse document frequencies and calculating tf-idf vectors. If you are looking to do something copmlex, LingPipe also provides methods to calculate LSA similarity between documents which gives better results than cosine similarity. For Python, you can use NLTK.