uda一个小题目吧，可以看一下，thank you!
通过网格搜索完善模型
在这个迷你 Lab 练习中，我们将为决策树模型拟合一些样本数据。 这个初始模型会过拟合。 然后，我们将使用网格搜索为这个模型找到更好的参数，以减少过拟合。
首先，导入：
%matplotlib inline
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
1.阅读并绘制数据
现在，这个函数将帮助我们读取 csv 文件并绘制数据。
def load_pts(csv_name):
data = np.asarray(pd.read_csv(csv_name, header=None))
X = data[:,0:2]
y = data[:,2]
plt.scatter(X[np.argwhere(y==0).flatten(),0], X[np.argwhere(y==0).flatten(),1],s = 50, color = 'blue', edgecolor = 'k')
plt.scatter(X[np.argwhere(y==1).flatten(),0], X[np.argwhere(y==1).flatten(),1],s = 50, color = 'red', edgecolor = 'k')
plt.xlim(-2.05,2.05)
plt.ylim(-2.05,2.05)
plt.grid(False)
plt.tick_params(
axis='x',
which='both',
bottom='off',
top='off')
return X,y
X, y = load_pts('data.csv')
plt.show()
png
该函数将帮助我们绘制模型。
def plot_model(X, y, clf):
plt.scatter(X[np.argwhere(y==0).flatten(),0],X[np.argwhere(y==0).flatten(),1],s = 50, color = 'blue', edgecolor = 'k')
plt.scatter(X[np.argwhere(y==1).flatten(),0],X[np.argwhere(y==1).flatten(),1],s = 50, color = 'red', edgecolor = 'k')
plt.xlim(-2.05,2.05)
plt.ylim(-2.05,2.05)
plt.grid(False)
plt.tick_params(
axis='x',
which='both',
bottom='off',
top='off')
r = np.linspace(-2.1,2.1,300)
s,t = np.meshgrid(r,r)
s = np.reshape(s,(np.size(s),1))
t = np.reshape(t,(np.size(t),1))
h = np.concatenate((s,t),1)
z = clf.predict(h)
s.shape = (np.size(r),np.size(r))
t.shape = (np.size(r),np.size(r))
z.shape = (np.size(r),np.size(r))
plt.contourf(s,t,z,colors = ['blue','red'],alpha = 0.2,levels = range(-1,2))
if len(np.unique(z)) > 1:
plt.contour(s,t,z,colors = 'k', linewidths = 2)
plt.show()
2. 将我们的数据分为训练和测试集
from sklearn.model_selection import train_test_split
from sklearn.metrics import f1_score, make_scorer
#Fixing a random seed
import random
random.seed(42)
# Split the data into training and testing sets
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
3. 拟合一个决策树模型
random_state=42
from sklearn.tree import DecisionTreeClassifier
# Define the model (with default hyperparameters)
clf = DecisionTreeClassifier(random_state=42)
# Fit the model
clf.fit(X_train, y_train)
# Make predictions using the unoptimized and model
train_predictions = clf.predict(X_train)
test_predictions = clf.predict(X_test)
Now let's plot the model, and find the testing f1_score, to see how we did.
plot_model(X, y, clf)
print('The Training F1 Score is', f1_score(train_predictions, y_train))
print('The Testing F1 Score is', f1_score(test_predictions, y_test))
The Training F1 Score is 1.0
The Testing F1 Score is 0.7
png
The Training F1 Score is 1.0
The Testing F1 Score is 0.7
File "<ipython-input-9-d0715772f77a>", line 1
The Training F1 Score is 1.0
^
SyntaxError: invalid syntax
# 现在有一些过拟合。 我们不仅仅是看图表，还需要看看高训练分（1.0）和低测试分（0.7）之间的差异。思考一下，我们是否可以找到更好的超参数来让这个模型做得更好？ 接下来我们将使用网格搜索。
下方几个小标题为解决过拟合方案。
### 4.（解决方案）使用网格搜索来完善模型
现在，我们将执行以下步骤：
1.首先，定义一些参数来执行网格搜索。 我们建议使用`max_depth`, `min_samples_leaf`, 和 `min_samples_split`。
2.使用`f1_score`，为模型制作记分器。
3.使用参数和记分器，在分类器上执行网格搜索。
4.将数据拟合到新的分类器中。
5.绘制模型并找到 f1_score。
6.如果模型不太好，请尝试更改参数的范围并再次拟合。
File "<ipython-input-10-71c8d92383eb>", line 6
现在，我们将执行以下步骤：
^
SyntaxError: invalid character in identifier
from sklearn.metrics import make_scorer
from sklearn.model_selection import GridSearchCV
clf = DecisionTreeClassifier(random_state=42)
# TODO: Create the parameters list you wish to tune.
parameters = {'max_depth':[2,4,6,8,10],'min_samples_leaf':[2,4,6,8,10], 'min_samples_split':[2,4,6,8,10]}
# TODO: Make an fbeta_score scoring object.
scorer = make_scorer(f1_score)
# TODO: Perform grid search on the classifier using 'scorer' as the scoring method.
grid_obj = GridSearchCV(clf, parameters, scoring=scorer)
# TODO: Fit the grid search object to the training data and find the optimal parameters.
grid_fit = grid_obj.fit(X_train, y_train)
# Get the estimator.
best_clf = grid_fit.best_estimator_
# Fit the new model.
best_clf.fit(X_train, y_train)
# Make predictions using the new model.
best_train_predictions = best_clf.predict(X_train)
best_test_predictions = best_clf.predict(X_test)
# Calculate the f1_score of the new model.
print('The training F1 Score is', f1_score(best_train_predictions, y_train))
print('The testing F1 Score is', f1_score(best_test_predictions, y_test))
# Plot the new model.
plot_model(X, y, best_clf)
# Let's also explore what parameters ended up being used in the new model.
#best_clf
The training F1 Score is 0.814814814815
The testing F1 Score is 0.8
The training F1 Score is 0.814814814815
The testing F1 Score is 0.8
File "<ipython-input-14-162f0fb3fffb>", line 1
The training F1 Score is 0.814814814815
^
SyntaxError: invalid syntax
png
DecisionTreeClassifier(class_weight=None, criterion='gini', max_depth=4,
max_features=None, max_leaf_nodes=None,
min_impurity_decrease=0.0, min_impurity_split=None,
min_samples_leaf=2, min_samples_split=2,
min_weight_fraction_leaf=0.0, presort=False, random_state=42,
splitter='best')
DecisionTreeClassifier(class_weight=None, criterion='gini', max_depth=4,
max_features=None, max_leaf_nodes=None,
min_impurity_decrease=0.0, min_impurity_split=None,
min_samples_leaf=2, min_samples_split=2,
min_weight_fraction_leaf=0.0, presort=False, random_state=42,
splitter='best')关于参数random_state：
参考：
https://stackoverflow.com/questions/28064634/random-state-pseudo-random-number-in-scikit-learn
这可能解释了经常使用的数字42： https://en.wikipedia.org/wiki/The_Hitchhiker%27s_Guide_to_the_Galaxy