我正在尝试在Python中实现k折交叉验证算法。我知道SKLearn提供了一个实现，但仍然...目前这是我的代码。
from sklearn import metrics
import numpy as np
class Cross_Validation:
@staticmethod
def partition(vector, fold, k):
size = vector.shape[0]
start = (size/k)*fold
end = (size/k)*(fold+1)
validation = vector[start:end]
if str(type(vector)) == "<class 'scipy.sparse.csr.csr_matrix'>":
indices = range(start, end)
mask = np.ones(vector.shape[0], dtype=bool)
mask[indices] = False
training = vector[mask]
elif str(type(vector)) == "<type 'numpy.ndarray'>":
training = np.concatenate((vector[:start], vector[end:]))
return training, validation
@staticmethod
def Cross_Validation(learner, k, examples, labels):
train_folds_score = []
validation_folds_score = []
for fold in range(0, k):
training_set, validation_set = Cross_Validation.partition(examples, fold, k)
training_labels, validation_labels = Cross_Validation.partition(labels, fold, k)
learner.fit(training_set, training_labels)
training_predicted = learner.predict(training_set)
validation_predicted = learner.predict(validation_set)
train_folds_score.append(metrics.accuracy_score(training_labels, training_predicted))
validation_folds_score.append(metrics.accuracy_score(validation_labels, validation_predicted))
return train_folds_score, validation_folds_score
learner参数是来自SKlearn库的分类器，k是交叉验证的折数，examples是由CountVectorizer（同样是SKlearn）生成的稀疏矩阵，它代表了词袋的表示方式。 例如：
from sklearn.feature_extraction.text import CountVectorizer
from sklearn.naive_bayes import MultinomialNB
from Cross_Validation import Cross_Validation as cv
vectorizer = CountVectorizer(stop_words='english', lowercase=True, min_df=2, analyzer="word")
data = vectorizer.fit_transform("""textual data""")
clfMNB = MultinomialNB(alpha=.0001)
score = cv.Cross_Validation(clfMNB, 10, data, labels)
print "Train score" + str(score[0])
print "Test score" + str(score[1])
我猜测由于某些逻辑错误导致模型在训练集上得分为95％（预期），但在测试集上几乎为0，但我找不到原因。
希望我表达清楚。 提前感谢。
这是加载文本并转换为可传递给向量化器的向量的代码。它还返回标签向量。
from nltk.tokenize import word_tokenize
from Categories_Data import categories
import numpy as np
import codecs
import glob
import os
import re
class Data_Preprocessor:
def tokenize(self, text):
tokens = word_tokenize(text)
alpha = [t for t in tokens if unicode(t).isalpha()]
return alpha
def header_not_fully_removed(self, text):
if ":" in text.splitlines()[0]:
return len(text.splitlines()[0].split(":")[0].split()) == 1
else:
return False
def strip_newsgroup_header(self, text):
_before, _blankline, after = text.partition('\n\n')
if len(after) > 0 and self.header_not_fully_removed(after):
after = self.strip_newsgroup_header(after)
return after
def strip_newsgroup_quoting(self, text):
_QUOTE_RE = re.compile(r'(writes in|writes:|wrote:|says:|said:'r'|^In article|^Quoted from|^\||^>)')
good_lines = [line for line in text.split('\n')
if not _QUOTE_RE.search(line)]
return '\n'.join(good_lines)
def strip_newsgroup_footer(self, text):
lines = text.strip().split('\n')
for line_num in range(len(lines) - 1, -1, -1):
line = lines[line_num]
if line.strip().strip('-') == '':
break
if line_num > 0:
return '\n'.join(lines[:line_num])
else:
return text
def raw_to_vector(self, path, to_be_stripped=["header", "footer", "quoting"], noise_threshold=-1):
base_dir = os.getcwd()
train_data = []
label_data = []
for category in categories:
os.chdir(base_dir)
os.chdir(path+"/"+category[0])
for filename in glob.glob("*"):
with codecs.open(filename, 'r', encoding='utf-8', errors='replace') as target:
data = target.read()
if "quoting" in to_be_stripped:
data = self.strip_newsgroup_quoting(data)
if "header" in to_be_stripped:
data = self.strip_newsgroup_header(data)
if "footer" in to_be_stripped:
data = self.strip_newsgroup_footer(data)
if len(data) > noise_threshold:
train_data.append(data)
label_data.append(category[1])
os.chdir(base_dir)
return np.array(train_data), np.array(label_data)
这是"from Categories_Data import categories"导入的内容...
categories = [
('alt.atheism',0),
('comp.graphics',1),
('comp.os.ms-windows.misc',2),
('comp.sys.ibm.pc.hardware',3),
('comp.sys.mac.hardware',4),
('comp.windows.x',5),
('misc.forsale',6),
('rec.autos',7),
('rec.motorcycles',8),
('rec.sport.baseball',9),
('rec.sport.hockey',10),
('sci.crypt',11),
('sci.electronics',12),
('sci.med',13),
('sci.space',14),
('soc.religion.christian',15),
('talk.politics.guns',16),
('talk.politics.mideast',17),
('talk.politics.misc',18),
('talk.religion.misc',19)
]
CountVectorizer中的代码？ - Pankaj Daga