使用 chi2 的 SelectKBest() 的 K 值
K value for SelectKBest() using chi2
我正在使用此处稍作修改的代码：集成方法：使用 Scikit-Learn 调整 XGBoost 模型
当我执行它时，我不断收到这个错误：
ValueError: k should be >=0, <= n_features = 4; got 10. Use k='all' to return all features.
我有四个特征和一个目标。我在 SeleckKBest() 函数的管道参数中的下面的代码中尝试了 k 的值 1-4，但同样的错误仍然存在。
这是我的可重现代码：
import pandas as pd
df = pd.DataFrame({'Number1': [11, 12, 13, 14, 15, 16, 17, 18, 19, 20],
'Color1': ['Red', 'Blue', 'Green', 'Yellow', 'Orange', 'Red',
'Blue', 'Green', 'Yellow', 'Orange'],
'Number2': [221, 222, 223, 224, 225, 226, 227, 228, 229,230],
'Trait1': ['Jogger', 'Sedentary', 'Tennis_Player', 'Graveyard', 'Shift_Worker', 'Jogger', 'Fulltime_Mom', 'Tennis_Player', 'Couch_Potato', 'Jogger', 'Graveyard_Shift_Worder'],
'Target': ['yes', 'no', 'yes', 'no', 'yes', 'no', 'yes', 'no', 'yes', 'no']})
col = pd.Categorical(df['Target'])
df['Target'] = col.codes
from sklearn.base import BaseEstimator, TransformerMixin
from sklearn.preprocessing import MinMaxScaler
class PreprocessTransformer(BaseEstimator, TransformerMixin):
def __init__(self, cat_features, num_features):
self.cat_features = cat_features
self.num_features = num_features
def fit(self, X, y=None):
return self
def transform(self, X, y=None):
df = X.copy()
# Convert columns to categorical
for name in self.cat_features:
col = pd.Categorical(df[name])
df[name] = col.codes
# Normalize numerical features
scaler = MinMaxScaler()
df[self.num_features] = scaler.fit_transform(df[self.num_features])
return df
from sklearn.model_selection import train_test_split
# Split the dataset into training and testing
X_train, X_test, y_train, y_test = train_test_split(
df.drop('Target', axis=1),
df['Target'],
test_size=0.2,
random_state=42,
shuffle=True,
stratify=df['Target']
)
from sklearn.pipeline import Pipeline
from sklearn.feature_selection import SelectKBest, chi2
import xgboost as xgb
# Get columns list for categorical and numerical
categorical_features = df.select_dtypes('object').columns.tolist()
numerical_features = df.select_dtypes('int64').columns.tolist()
# Create a pipeline
pipe = Pipeline([
('preproc', PreprocessTransformer(categorical_features, numerical_features)),
('fs', SelectKBest(k=0)),
('clf', xgb.XGBClassifier(objective='binary:logistic'))
])
from sklearn.model_selection import KFold, GridSearchCV
from sklearn.metrics import accuracy_score, make_scorer
# Define our search space for grid search
search_space = [
{
'clf__n_estimators': [50, 100, 150, 200],
'clf__learning_rate': [0.01, 0.1, 0.2, 0.3],
'clf__max_depth': range(3, 10),
'clf__colsample_bytree': [i/10.0 for i in range(1, 3)],
'clf__gamma': [i/10.0 for i in range(3)],
'fs__score_func': [chi2],
'fs__k': [10],
}
]
# Define cross validation
kfold = KFold(n_splits=8, random_state=42)
# AUC and accuracy as score
scoring = {'AUC':'roc_auc', 'Accuracy':make_scorer(accuracy_score)}
# Define grid search
grid = GridSearchCV(
pipe,
param_grid=search_space,
cv=kfold,
scoring=scoring,
refit='AUC',
verbose=1,
n_jobs=-1
)
# Fit grid search
model = grid.fit(X_train, y_train)
错误：
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-84-5c30ee0bb39f> in <module>
28 )
29 # Fit grid search
---> 30 model = grid.fit(X_train, y_train)
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/model_selection/_search.py in fit(self, X, y, groups, **fit_params)
737 refit_start_time = time.time()
738 if y is not None:
--> 739 self.best_estimator_.fit(X, y, **fit_params)
740 else:
741 self.best_estimator_.fit(X, **fit_params)
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/pipeline.py in fit(self, X, y, **fit_params)
348 This estimator
349 """
--> 350 Xt, fit_params = self._fit(X, y, **fit_params)
351 with _print_elapsed_time('Pipeline',
352 self._log_message(len(self.steps) - 1)):
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/pipeline.py in _fit(self, X, y, **fit_params)
313 message_clsname='Pipeline',
314 message=self._log_message(step_idx),
--> 315 **fit_params_steps[name])
316 # Replace the transformer of the step with the fitted
317 # transformer. This is necessary when loading the transformer
~/anaconda3/envs/python3/lib/python3.6/site-packages/joblib/memory.py in __call__(self, *args, **kwargs)
353
354 def __call__(self, *args, **kwargs):
--> 355 return self.func(*args, **kwargs)
356
357 def call_and_shelve(self, *args, **kwargs):
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/pipeline.py in _fit_transform_one(transformer, X, y, weight, message_clsname, message, **fit_params)
726 with _print_elapsed_time(message_clsname, message):
727 if hasattr(transformer, 'fit_transform'):
--> 728 res = transformer.fit_transform(X, y, **fit_params)
729 else:
730 res = transformer.fit(X, y, **fit_params).transform(X)
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/base.py in fit_transform(self, X, y, **fit_params)
572 else:
573 # fit method of arity 2 (supervised transformation)
--> 574 return self.fit(X, y, **fit_params).transform(X)
575
576
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/feature_selection/_univariate_selection.py in fit(self, X, y)
346 % (self.score_func, type(self.score_func)))
347
--> 348 self._check_params(X, y)
349 score_func_ret = self.score_func(X, y)
350 if isinstance(score_func_ret, (list, tuple)):
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/feature_selection/_univariate_selection.py in _check_params(self, X, y)
512 raise ValueError("k should be >=0, <= n_features = %d; got %r. "
513 "Use k='all' to return all features."
--> 514 % (X.shape[1], self.k))
515
516 def _get_support_mask(self):
ValueError: k should be >=0, <= n_features = 4; got 10. Use k='all' to return all features.
有 4 个特征（Number1、Color1、Number2、Trait1）。
SelectKBest 将 select 原始集中的 K 最能解释的特征，因此 K 应该是一个大于 0 且小于 0 的值或等于特征总数。
您正在将 GridSearch 对象设置为在该行中始终使用 10：
'fs__k': [10]
这会覆盖您在声明期间的定义
('fs', SelectKBest(k=0)),
您可以删除 fs__k 行并将声明行更正为您想要的 k，或者在 search_grid 定义中设置您想要的 k。
我正在使用此处稍作修改的代码：集成方法：使用 Scikit-Learn 调整 XGBoost 模型
当我执行它时，我不断收到这个错误：
ValueError: k should be >=0, <= n_features = 4; got 10. Use k='all' to return all features.
我有四个特征和一个目标。我在 SeleckKBest() 函数的管道参数中的下面的代码中尝试了 k 的值 1-4，但同样的错误仍然存在。
这是我的可重现代码：
import pandas as pd
df = pd.DataFrame({'Number1': [11, 12, 13, 14, 15, 16, 17, 18, 19, 20],
'Color1': ['Red', 'Blue', 'Green', 'Yellow', 'Orange', 'Red',
'Blue', 'Green', 'Yellow', 'Orange'],
'Number2': [221, 222, 223, 224, 225, 226, 227, 228, 229,230],
'Trait1': ['Jogger', 'Sedentary', 'Tennis_Player', 'Graveyard', 'Shift_Worker', 'Jogger', 'Fulltime_Mom', 'Tennis_Player', 'Couch_Potato', 'Jogger', 'Graveyard_Shift_Worder'],
'Target': ['yes', 'no', 'yes', 'no', 'yes', 'no', 'yes', 'no', 'yes', 'no']})
col = pd.Categorical(df['Target'])
df['Target'] = col.codes
from sklearn.base import BaseEstimator, TransformerMixin
from sklearn.preprocessing import MinMaxScaler
class PreprocessTransformer(BaseEstimator, TransformerMixin):
def __init__(self, cat_features, num_features):
self.cat_features = cat_features
self.num_features = num_features
def fit(self, X, y=None):
return self
def transform(self, X, y=None):
df = X.copy()
# Convert columns to categorical
for name in self.cat_features:
col = pd.Categorical(df[name])
df[name] = col.codes
# Normalize numerical features
scaler = MinMaxScaler()
df[self.num_features] = scaler.fit_transform(df[self.num_features])
return df
from sklearn.model_selection import train_test_split
# Split the dataset into training and testing
X_train, X_test, y_train, y_test = train_test_split(
df.drop('Target', axis=1),
df['Target'],
test_size=0.2,
random_state=42,
shuffle=True,
stratify=df['Target']
)
from sklearn.pipeline import Pipeline
from sklearn.feature_selection import SelectKBest, chi2
import xgboost as xgb
# Get columns list for categorical and numerical
categorical_features = df.select_dtypes('object').columns.tolist()
numerical_features = df.select_dtypes('int64').columns.tolist()
# Create a pipeline
pipe = Pipeline([
('preproc', PreprocessTransformer(categorical_features, numerical_features)),
('fs', SelectKBest(k=0)),
('clf', xgb.XGBClassifier(objective='binary:logistic'))
])
from sklearn.model_selection import KFold, GridSearchCV
from sklearn.metrics import accuracy_score, make_scorer
# Define our search space for grid search
search_space = [
{
'clf__n_estimators': [50, 100, 150, 200],
'clf__learning_rate': [0.01, 0.1, 0.2, 0.3],
'clf__max_depth': range(3, 10),
'clf__colsample_bytree': [i/10.0 for i in range(1, 3)],
'clf__gamma': [i/10.0 for i in range(3)],
'fs__score_func': [chi2],
'fs__k': [10],
}
]
# Define cross validation
kfold = KFold(n_splits=8, random_state=42)
# AUC and accuracy as score
scoring = {'AUC':'roc_auc', 'Accuracy':make_scorer(accuracy_score)}
# Define grid search
grid = GridSearchCV(
pipe,
param_grid=search_space,
cv=kfold,
scoring=scoring,
refit='AUC',
verbose=1,
n_jobs=-1
)
# Fit grid search
model = grid.fit(X_train, y_train)
错误：
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-84-5c30ee0bb39f> in <module>
28 )
29 # Fit grid search
---> 30 model = grid.fit(X_train, y_train)
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/model_selection/_search.py in fit(self, X, y, groups, **fit_params)
737 refit_start_time = time.time()
738 if y is not None:
--> 739 self.best_estimator_.fit(X, y, **fit_params)
740 else:
741 self.best_estimator_.fit(X, **fit_params)
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/pipeline.py in fit(self, X, y, **fit_params)
348 This estimator
349 """
--> 350 Xt, fit_params = self._fit(X, y, **fit_params)
351 with _print_elapsed_time('Pipeline',
352 self._log_message(len(self.steps) - 1)):
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/pipeline.py in _fit(self, X, y, **fit_params)
313 message_clsname='Pipeline',
314 message=self._log_message(step_idx),
--> 315 **fit_params_steps[name])
316 # Replace the transformer of the step with the fitted
317 # transformer. This is necessary when loading the transformer
~/anaconda3/envs/python3/lib/python3.6/site-packages/joblib/memory.py in __call__(self, *args, **kwargs)
353
354 def __call__(self, *args, **kwargs):
--> 355 return self.func(*args, **kwargs)
356
357 def call_and_shelve(self, *args, **kwargs):
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/pipeline.py in _fit_transform_one(transformer, X, y, weight, message_clsname, message, **fit_params)
726 with _print_elapsed_time(message_clsname, message):
727 if hasattr(transformer, 'fit_transform'):
--> 728 res = transformer.fit_transform(X, y, **fit_params)
729 else:
730 res = transformer.fit(X, y, **fit_params).transform(X)
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/base.py in fit_transform(self, X, y, **fit_params)
572 else:
573 # fit method of arity 2 (supervised transformation)
--> 574 return self.fit(X, y, **fit_params).transform(X)
575
576
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/feature_selection/_univariate_selection.py in fit(self, X, y)
346 % (self.score_func, type(self.score_func)))
347
--> 348 self._check_params(X, y)
349 score_func_ret = self.score_func(X, y)
350 if isinstance(score_func_ret, (list, tuple)):
~/anaconda3/envs/python3/lib/python3.6/site-packages/sklearn/feature_selection/_univariate_selection.py in _check_params(self, X, y)
512 raise ValueError("k should be >=0, <= n_features = %d; got %r. "
513 "Use k='all' to return all features."
--> 514 % (X.shape[1], self.k))
515
516 def _get_support_mask(self):
ValueError: k should be >=0, <= n_features = 4; got 10. Use k='all' to return all features.
有 4 个特征（Number1、Color1、Number2、Trait1）。
SelectKBest 将 select 原始集中的 K 最能解释的特征，因此 K 应该是一个大于 0 且小于 0 的值或等于特征总数。
您正在将 GridSearch 对象设置为在该行中始终使用 10：
'fs__k': [10]
这会覆盖您在声明期间的定义
('fs', SelectKBest(k=0)),
您可以删除 fs__k 行并将声明行更正为您想要的 k，或者在 search_grid 定义中设置您想要的 k。