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

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

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

I am combining the solutions from answers of @FredFoo and @Renaud. My solution is able to apply @Renaud's preprocessing on the text corpus of @FredFoo and then display pairwise similarities where the similarity is greater than 0. I ran this code on Windows by installing python and pip first. pip is installed as part of python but you may have to explicitly do it by re-running the installation package, choosing modify and then choosing pip. I use the command line to execute my python code saved in a file "similarity.py". I had to execute the following commands:

>set PYTHONPATH=%PYTHONPATH%;C:\_location_of_python_lib_
>python -m pip install sklearn
>python -m pip install nltk
>py similarity.py

similar .py的代码如下:

from sklearn.feature_extraction.text import TfidfVectorizer
import nltk, string
import numpy as np
nltk.download('punkt') # if necessary...

stemmer = nltk.stem.porter.PorterStemmer()
remove_punctuation_map = dict((ord(char), None) for char in string.punctuation)

def stem_tokens(tokens):
    return [stemmer.stem(item) for item in tokens]

def normalize(text):
    return stem_tokens(nltk.word_tokenize(text.lower().translate(remove_punctuation_map)))

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(tokenizer=normalize, stop_words='english')
tfidf = vect.fit_transform(corpus)   
                                                                                                                                                                                                                    
pairwise_similarity = tfidf * tfidf.T

#view the pairwise similarities 
print(pairwise_similarity)

#check how a string is normalized
print(normalize("The scikit-learn docs are Orange and Blue"))

为了用更少的数据集找到句子的相似性，并获得更高的精度，你可以使用下面的python包，它使用预训练的BERT模型，

pip install similar-sentences

如果你正在寻找一些非常精确的东西，你需要使用一些比tf-idf更好的工具。通用句子编码器是最准确的找到任何两段文本之间的相似性的编码器之一。谷歌提供了预训练的模型，您可以将其用于自己的应用程序，而不需要从头开始训练任何东西。首先，你必须安装tensorflow和tensorflow-hub:

    pip install tensorflow
    pip install tensorflow_hub

下面的代码允许您将任何文本转换为固定长度的向量表示，然后您可以使用点积来找出它们之间的相似性

import tensorflow_hub as hub
module_url = "https://tfhub.dev/google/universal-sentence-encoder/1?tf-hub-format=compressed"

# Import the Universal Sentence Encoder's TF Hub module
embed = hub.Module(module_url)

# sample text
messages = [
# Smartphones
"My phone is not good.",
"Your cellphone looks great.",

# Weather
"Will it snow tomorrow?",
"Recently a lot of hurricanes have hit the US",

# Food and health
"An apple a day, keeps the doctors away",
"Eating strawberries is healthy",
]

similarity_input_placeholder = tf.placeholder(tf.string, shape=(None))
similarity_message_encodings = embed(similarity_input_placeholder)
with tf.Session() as session:
    session.run(tf.global_variables_initializer())
    session.run(tf.tables_initializer())
    message_embeddings_ = session.run(similarity_message_encodings, feed_dict={similarity_input_placeholder: messages})

    corr = np.inner(message_embeddings_, message_embeddings_)
    print(corr)
    heatmap(messages, messages, corr)

绘图的代码:

def heatmap(x_labels, y_labels, values):
    fig, ax = plt.subplots()
    im = ax.imshow(values)

    # We want to show all ticks...
    ax.set_xticks(np.arange(len(x_labels)))
    ax.set_yticks(np.arange(len(y_labels)))
    # ... and label them with the respective list entries
    ax.set_xticklabels(x_labels)
    ax.set_yticklabels(y_labels)

    # Rotate the tick labels and set their alignment.
    plt.setp(ax.get_xticklabels(), rotation=45, ha="right", fontsize=10,
         rotation_mode="anchor")

    # Loop over data dimensions and create text annotations.
    for i in range(len(y_labels)):
        for j in range(len(x_labels)):
            text = ax.text(j, i, "%.2f"%values[i, j],
                           ha="center", va="center", color="w", 
fontsize=6)

    fig.tight_layout()
    plt.show()

结果将是:

正如你所看到的，最相似的是文本本身和意义相近的文本之间。

重要的是:第一次运行代码会很慢，因为它需要下载模型。如果你想防止它再次下载模型并使用本地模型，你必须为缓存创建一个文件夹，并将其添加到环境变量中，然后在第一次运行后使用该路径:

tf_hub_cache_dir = "universal_encoder_cached/"
os.environ["TFHUB_CACHE_DIR"] = tf_hub_cache_dir

# pointing to the folder inside cache dir, it will be unique on your system
module_url = tf_hub_cache_dir+"/d8fbeb5c580e50f975ef73e80bebba9654228449/"
embed = hub.Module(module_url)

更多信息:https://tfhub.dev/google/universal-sentence-encoder/2