1、原理
文本相似度的度量有很多種方法,特定詞出現頻度,整體文本風格等。本文將使用tf-idf方式,通過cosin相似度度量兩個文本的相似度。 tf爲詞頻代表token frequence idf爲你文檔頻率,代表(所有文檔的數目)/包含 該單詞的文檔出現頻率)
1+log(doc_num/doc_contain_thisWord_num)
每個單詞的詞頻逆文檔頻率的計算方法爲tf[word] * idf[word]
將所有文檔中的單詞構成一個詞典,每個單詞用t用一個長度爲len(文檔數)的向量表示,向量中的每一個值具體表示含義如下:如果該單詞出現在文檔中就用tf-idf值替代當前詞,如果該單詞未出現在該文檔中則用0表示。
文本相似度可以表示爲:
2、代碼
這段代碼我就不添加太多註釋了,大多可以直接理解的。import nltk
import math
from sklearn.feature_extraction.text import TfidfVectorizer
from sklearn.metrics.pairwise import cosine_similarity
#創建類
class TextSimilarityExample:
#定義屬性
def __init__(self):
self.statments = [
"ruled india",
"So many kindom rlued india",
"Chalukyas ruled inda",
"your kindom is a good king"
]
#獲取詞頻tokenFrequence字典
def TF(self, sentence):
words = nltk.word_tokenize(sentence.lower())
freq = nltk.FreqDist(words)
dictionary = {}
for key in freq.keys():
norm = freq[key]/ float(len(words))
dictionary[key] = norm
return dictionary
#獲取逆文檔頻率
def IDF(self):
def idf(TotalNumberOfDocuments, NumberOfDocumentWithThisWord):
return 1.0 - math.log(TotalNumberOfDocuments/NumberOfDocumentWithThisWord)
numberOfDoc = len(self.statments)
uniqueWords = {}
idfValues = {}
for sentence in self.statments:
for word in nltk.word_tokenize(sentence.lower()):
if word not in uniqueWords:
uniqueWords[word] = 1
else:
uniqueWords[word] += 1
for word in uniqueWords:
idfValues[word] = idf(numberOfDoc, uniqueWords[word])
return idfValues
#根據公式得到詞頻逆文檔頻率
def TF_IDF(self, query):
words = nltk.word_tokenize(query.lower())
idf = self.IDF()
vectors = {}
for sentence in self.statments:
tf = self.TF(sentence)
for word in words:
tfv = tf[word] if word in tf else 0.0
idfv = idf[word] if word in idf else 0.0
mul = tfv * idfv
if word not in vectors:
vectors[word] = []
vectors[word].append(mul)
return vectors
def displayVectors(self, vectors):
print(self.statments)
for word in vectors:
print("{} --> {}".format(word, vectors[word]))
def cosineSimilarity(self):
vec = TfidfVectorizer()
matrix = vec.fit_transform(self.statments)
for j in range(1,5):
i = j -1
print("\t similarity of document {} with others".format(i))
similarity = cosine_similarity(matrix[i:j], matrix)
print(similarity)
def demo(self):
query = self.statments[0]
vec = self.TF_IDF(query)
self.displayVectors(vec)
self.cosineSimilarity()
if __name__ == "__main__":
ts = TextSimilarityExample()
ts.demo()