[英]How to use sklearn TfidfVectorizer fit_transform on two columns
[英]How fit_transform, transform and TfidfVectorizer works
我正在做一個模糊匹配項目,我發現了一個非常有趣的方法:awesome_cossim_top
我全局理解定義,但不明白當我們做 fit_transform 時發生了什么
import pandas as pd
import sqlite3 as sql
from sklearn.feature_extraction.text import TfidfVectorizer
import numpy as np
from scipy.sparse import csr_matrix
import sparse_dot_topn.sparse_dot_topn as ct
import re
def ngrams(string, n=3):
string = re.sub(r'[,-./]|\sBD',r'', re.sub(' +', ' ',str(string)))
ngrams = zip(*[string[i:] for i in range(n)])
return [''.join(ngram) for ngram in ngrams]
def awesome_cossim_top(A, B, ntop, lower_bound=0):
# force A and B as a CSR matrix.
# If they have already been CSR, there is no overhead
A = A.tocsr()
B = B.tocsr()
M, _ = A.shape
_, N = B.shape
idx_dtype = np.int32
nnz_max = M*ntop
indptr = np.zeros(M+1, dtype=idx_dtype)
indices = np.zeros(nnz_max, dtype=idx_dtype)
data = np.zeros(nnz_max, dtype=A.dtype)
ct.sparse_dot_topn(
M, N, np.asarray(A.indptr, dtype=idx_dtype),
np.asarray(A.indices, dtype=idx_dtype),
A.data,
np.asarray(B.indptr, dtype=idx_dtype),
np.asarray(B.indices, dtype=idx_dtype),
B.data,
ntop,
lower_bound,
indptr, indices, data)
print('ct.sparse_dot_topn: ', ct.sparse_dot_topn)
return csr_matrix((data,indices,indptr),shape=(M,N))
def get_matches_df(sparse_matrix, A, B, top=100):
non_zeros = sparse_matrix.nonzero()
sparserows = non_zeros[0]
sparsecols = non_zeros[1]
if top:
nr_matches = top
else:
nr_matches = sparsecols.size
left_side = np.empty([nr_matches], dtype=object)
right_side = np.empty([nr_matches], dtype=object)
similairity = np.zeros(nr_matches)
for index in range(0, nr_matches):
left_side[index] = A[sparserows[index]]
right_side[index] = B[sparsecols[index]]
similairity[index] = sparse_matrix.data[index]
return pd.DataFrame({'left_side': left_side,
'right_side': right_side,
'similairity': similairity})
這是我遇到困惑的腳本:為什么我們應該先使用 fit_transform 然后只使用 SAME 矢量化器進行轉換。 我試圖從向量化器和矩陣打印一些輸出,如 print(vectorizer.get_feature_names()) 但不理解邏輯。
有人可以幫我澄清一下嗎?
非常感謝 !!
Col_clean = 'fruits_normalized'
Col_dirty = 'fruits'
#read table
data_dirty={f'{Col_dirty}':['I am an apple', 'You are an apple', 'Aple', 'Appls', 'Apples']}
data_clean= {f'{Col_clean}':['apple', 'pear', 'banana', 'apricot', 'pineapple']}
df_clean = pd.DataFrame(data_clean)
df_dirty = pd.DataFrame(data_dirty)
Name_clean = df_clean[f'{Col_clean}'].unique()
Name_dirty= df_dirty[f'{Col_dirty}'].unique()
vectorizer = TfidfVectorizer(min_df=1, analyzer=ngrams)
clean_idf_matrix = vectorizer.fit_transform(Name_clean)
dirty_idf_matrix = vectorizer.transform(Name_dirty)
matches = awesome_cossim_top(dirty_idf_matrix, clean_idf_matrix.transpose(),1,0)
matches_df = get_matches_df(matches, Name_dirty, Name_clean, top = 0)
with pd.option_context('display.max_rows', None, 'display.max_columns', None):
matches_df.to_excel("output_apple.xlsx")
print('done')
TfidfVectorizer.fit_transform
用於從訓練數據集創建詞匯表, TfidfVectorizer.transform
用於將該詞匯表映射到測試數據集,以便測試數據中的特征數量與訓練數據相同。 下面的例子可能會有所幫助:
import pandas as pd
from sklearn.feature_extraction.text import TfidfVectorizer
創建一個虛擬訓練數據:
train = pd.DataFrame({'Text' :['I am a data scientist','Cricket is my favorite sport', 'I work on Python regularly', 'Python is very fast for data mining', 'I love playing cricket'],
'Category' :['Data_Science','Cricket','Data_Science','Data_Science','Cricket']})
還有一個小測試數據:
test = pd.DataFrame({'Text' :['I am new to data science field', 'I play cricket on weekends', 'I like writing Python codes'],
'Category' :['Data_Science','Cricket','Data_Science']})
創建一個名為vectorizer
的TfidfVectorizer()
對象
vectorizer = TfidfVectorizer()
將其擬合到火車數據上
X_train = vectorizer.fit_transform(train['Text'])
print(vectorizer.get_feature_names())
#['am', 'cricket', 'data', 'fast', 'favorite', 'for', 'is', 'love', 'mining', 'my', 'on', 'playing', 'python', 'regularly', 'scientist', 'sport', 'very', 'work']
feature_names = vectorizer.get_feature_names()
df= pd.DataFrame(X.toarray(),columns=feature_names)
現在看看如果你在測試數據集上做同樣的事情會發生什么:
vectorizer_test = TfidfVectorizer()
X_test = vectorizer_test.fit_transform(test['Text'])
print(vectorizer_test.get_feature_names())
#['am', 'codes', 'cricket', 'data', 'field', 'like', 'new', 'on', 'play', 'python', 'science', 'to', 'weekends', 'writing']
feature_names_test = vectorizer_test.get_feature_names()
df_test= pd.DataFrame(X_test.toarray(),columns = feature_names_test)
它使用測試數據集創建了另一個詞匯表,與來自訓練數據的 18 個詞(列)相比,它有 14 個唯一的詞(列)。
現在,如果您在訓練數據上訓練機器學習算法進行text-classification
並嘗試根據測試數據對矩陣進行預測,它將失敗並產生錯誤,即訓練數據和測試數據之間的特征不同。
為了克服這個錯誤,我們在text-classification
做這樣的事情:
X_test_from_train = vectorizer.transform(test['Text'])
feature_names_test_from_train = vectorizer.get_feature_names()
df_test_from_train = pd.DataFrame(X_test_from_train.toarray(),columns = feature_names_test_from_train)
在這里你會注意到我們沒有使用fit_transform
命令,而是對測試數據使用了transform
,原因相同,在對測試數據進行預測時,我們只想使用在訓練和測試中相似的特征數據,以便我們沒有特征不匹配錯誤。
希望這可以幫助!!
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.