机器学习第2章端到端的机器学习项目

机器学习实战：基于Scikit-Learn和TensorFlow的笔记

参考：作者的Jupyter Notebook
Chapter 2 – End-to-end Machine Learning project

下载数据

打开vscode，建立新的python文件，输入以下代码，下载housing.tgz文件，并将housing.csv解压到这个目录

import os
import tarfile
from six.moves import urllib

download_root = "https://raw.githubusercontent.com/ageron/handson-ml/master/"
HOUSING_PATH = "datasets/housing"
HOUSING_URL = download_root + HOUSING_PATH + "/housing.tgz"

def fetch_housing_data(housing_url=HOUSING_URL,housing_path=HOUSING_PATH):
    if not os.path.isdir(housing_path):
        os.makedirs(housing_path)
    tgz_path = os.path.join(housing_path, "housing.tgz")
    urllib.request.urlretrieve(housing_url, tgz_path)
    housing_tgz = tarfile.open(tgz_path)
    housing_tgz.extractall(path=housing_path)
    housing_tgz.close()

fetch_housing_data()

下载后可将函数注释

快速查看数据结构

使用pandas加载数据

mport pandas as pd
def load_housing_data(housing_path=HOUSING_PATH):
  csv_path = os.path.join(housing_path, "housing.csv")
  return pd.read_csv(csv_path)
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函数返回一个包含所有数据的Pandas DataFrame对象

调用DataFrames的head()方法查看前5行数据（由于使用的是vscode所以会和书里有所不同）,查看完可注释
housing = load_housing_data()
print(housing.head())
总共有10个属性

通过info（）方法可以快速获取数据集的简单描述，特别是总行数、每个属性的类型和非空值的数量
print(housing.info())

使用value_counts（）方法查看有多少种分类存在，每种类别下分别有多少个区域
print(housing[“ocean_proximity”].value_counts())

通过describe（）方法可以显示数值属性的摘要
print(housing.describe())

在整个数据集上调用hist（）方法，绘制每个属性的直方图

import matplotlib.pyplot as plt
housing.hist(bins=50, figsize=(50,15))
plt.show()
创建测试集

理论上，创建测试集非常简单：只需要随机选择一些实例，通常是数据集的20%，然后将它们放在一边：

import numpy as np
def split_train_test(data, test_ratio):
    shuffled_indices = np.random.permutation(len(data))
    test_set_size = int(len(data) * test_ratio)
    test_indices = shuffled_indices[:test_set_size]
    train_indices = shuffled_indices[test_set_size:]
    return data.iloc[train_indices], data.iloc[test_indices]

train_set, test_set = split_train_test(housing, 0.2)
print(len(train_set), "train +", len(test_set), "test")
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但这并不完美：如果你再运行一遍，它又会产生一个不同的数据集！这样下去，你（或者是你的机器学习算法）将会看到整个完整的数据集，而这正是创建测试集时需要避免的。常见的解决办法是每python基础教程个实例都使用一个标识符（identifier）来决定是否进入测试集（假定每个实例都有一个唯一且不变的标识符）

import hashlib
def test_set_check(identifier,test_ratio, hash):
    return hash(np.int64(identifier)).digest()[-1] < 256 * test_ratio

def split_train_test_by_id(data, test_ratio, id_column, hash=hashlib.md5):
    ids = data[id_column]
    in_test_set = ids.apply(lambda id_: test_set_check(id_, test_ratio, hash))
    return data.loc[~in_test_set], data.loc[in_test_set]

#housing_with_id = housing.reset_index()
#housing_with_id["id"] = housing["longitude"] * 1000 + housing["latitude"]
#train_set, test_set = split_train_test_by_id(housing_with_id, 0.2, "id")
from sklearn.model_selection import train_test_split
train_set, test_set = train_test_split(housing, test_size=0.2, random=42)
分层抽样
housing["income_cat"] = np.ceil(housing["median_income"] / 1.5)
housing["income_cat"].where(housing["income_cat"] < 5, 5.0, inplace=True)
from sklearn.model_selection import StratifiedShuffleSplit
split = StratifiedShuffleSplit(n_splits=1, test_size=0.2, random_state=42)
for train_index, test_index in split.split(housing, housing["income_cat"]):
    strat_train_set = housing.loc[train_index]
    strat_test_set = housing.loc[test_index]
print(housing["income_cat"].value_counts() / len(housing))
for set in (strat_train_set, strat_test_set):
    set.drop(["income_cat"], axis=1, inplace=True)
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数据探索和可视化

创建一个副本housing = strat_train_set.copy()
将地理数据可视化

#housing.plot(kind="scatter", x="longitude", y="latitude")
#housing.plot(kind="scatter", x="longitude", y="latitude", alpha=0.1)
housing.plot(kind="scatter", x="longitude", y="latitude", alpha=0.4,
s=housing["population"] / 100, label="population",
c="median_house_value", cmap=plt.get_cmap("jet"), colorbar=True,)
plt.legend()
plt.show()
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寻找相关性

#corr_matrix = housing.corr()
#print(corr_matrix["median_house_value"].sort_values(ascending=False))
from pandas.plotting import scatter_matrix #少了tools
attributes = ["median_house_value", "median_income", "total_rooms", "housing_median_age"]
scatter_matrix(housing[attributes], figsize=(12, 8))
housing.plot(kind="scatter", x="median_income", y="median_house_value", alpha=0.1)
plt.show()
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试验不同属性的组合

housing["rooms_per_household"] = housing["total_rooms"]/housing["households"]
housing["bedrooms_per_room"] = housing["total_bedrooms"]/housing["total_rooms"]
housing["population_per_household"]=housing["population"]/housing["households"]
corr_matrix = housing.corr()
print(corr_matrix["median_house_value"].sort_values(ascending=False))
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机器学习算法的数据准备

housing = strat_train_set.drop("median_house_value", axis=1)
housing_labels = strat_train_set["median_house_value"].copy()
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数据清理4选1

#housing.dropna(subset=["total_bedrooms"])    # option 1
#housing.drop("total_bedrooms", axis=1)       # option 2
#median = housing["total_bedrooms"].median()
#housing["total_bedrooms"].fillna(median)     # option 3

#option4: Scikit-Learn提供的imputer, 指定你要用属性的中位数值替换该属性的缺失值
from sklearn.impute import SimpleImputer #与书中不同，进化了
imputer = SimpleImputer(strategy="median")   #创建一个imputer实例
housing_num = housing.drop("ocean_proximity", axis=1)   #创建一个没有文本属性的数据副本ocean_proximity
imputer.fit(housing_num)   #使用fit（）方法将imputer实例适配到训练集
#print(imputer.statistics_)
#print(housing_num.median().values)
X = imputer.transform(housing_num)   #替换
housing_tr = pd.DataFrame(X, columns=housing_num.columns)   #放回Pandas DataFrame
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处理文本和分类属性

#先将这些文本标签转化为数字，Scikit-Learn为这类任务提供了一个转换器LabelEncoder：
from sklearn.preprocessing import LabelEncoder
encoder = LabelEncoder()
housing_cat = housing["ocean_proximity"]
housing_cat_encoded = encoder.fit_transform(housing_cat)
#print(housing_cat_encoded)
#print(encoder.classes_)

#Scikit-Learn提供了一个OneHotEncoder编码器，可以将整数分类值转换为独热向量
from sklearn.preprocessing import OneHotEncoder
encoder = OneHotEncoder()
housing_cat_1hot = encoder.fit_transform(housing_cat_encoded.reshape(-1,1))
#print(housing_cat_1hot.toarray())

#使用LabelBinarizer类可以一次性完成两个转换
from sklearn.preprocessing import LabelBinarizer
encoder = LabelBinarizer()
housing_cat_1hot = encoder.fit_transform(housing_cat)
print(housing_cat_1hot)
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自定义转换器

from sklearn.base import BaseEstimator, TransformerMixin
rooms_ix, bedrooms_ix, population_ix, household_ix = 3, 4, 5, 6
class CombinedAttributesAdder(BaseEstimator, TransformerMixin):
    def __init__(self, add_bedrooms_per_room = True): # no *args or **kargs
        self.add_bedrooms_per_room = add_bedrooms_per_room
    def fit(self, X, y=None):
        return self    #nothing else to do
    def transform(self, X, y=None):
        rooms_per_household = X[:, rooms_ix] / X[:, household_ix]
        population_per_household = X[:, population_ix] / X[:, household_ix]
        if self.add_bedrooms_per_room:
            bedrooms_per_room = X[:, bedrooms_ix] / X[:, rooms_ix]
            return np.c_[X, rooms_per_household, population_per_household,bedrooms_per_room]
        else:
            return np.c_[X, rooms_per_household, population_per_household]
attr_adder = CombinedAttributesAdder(add_bedrooms_per_room=False)
housing_extra_attribs = attr_adder.transform(housing.values)
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转换流水线

from sklearn.pipeline import Pipeline
from sklearn.preprocessing import StandardScaler
num_pipeline = Pipeline([
    ('imputer', SimpleImputer(strategy="median")),
    ('attribs_adder', CombinedAttributesAdder()),
    ('std_scaler', StandardScaler()),
    ])
housing_num_tr = num_pipeline.fit_transform(housing_num)
#print(housing_num_tr)

from sklearn.compose import ColumnTransformer
num_attribs = list(housing_num)
cat_attribs = ["ocean_proximity"]

full_pipeline = ColumnTransformer([
    ("num", num_pipeline, num_attribs),
    ("cat", OneHotEncoder(), cat_attribs),
])

housing_prepared = full_pipeline.fit_transform(housing)
#print(housing_prepared)
#print(housing_prepared.shape)
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选择和训练模型

训练一个线性回归模型：

from sklearn.linear_model import LinearRegression
lin_reg = LinearRegression()
lin_reg.fit(housing_prepared, housing_labels)
#print(lin_reg)
#实例试试
some_data = housing.iloc[:5]
some_labels = housing_labels.iloc[:5]
some_data_prepared = full_pipeline.transform(some_data)
#print("Predictions:", lin_reg.predict(some_data_prepared))
#print("Labels:", list(some_labels))
#print(some_data_prepared)
使用Scikit-Learn的mean_squared_error函数来测量整个训练集上回归模型的RMSE：
from sklearn.metrics import mean_squared_error
housing_predictions = lin_reg.predict(housing_prepared)
lin_mse = mean_squared_error(housing_labels, housing_predictions)
lin_rmse = np.sqrt(lin_mse)
#print(lin_rmse)
from sklearn.metrics import mean_absolute_error
lin_mae = mean_absolute_error(housing_labels, housing_predictions)
#print(lin_mae)
我们来训练一个(决策树)DecisionTreeRegressor。
from sklearn.tree import DecisionTreeRegressor
tree_reg = DecisionTreeRegressor(random_state=42)
tree_reg.fit(housing_prepared, housing_labels)
housing_predictions = tree_reg.predict(housing_prepared)
tree_mse = mean_squared_error(housing_labels, housing_predictions)
tree_rmse = np.sqrt(tree_mse)
#print(tree_rmse)    #可能对数据严重过度拟合
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使用交叉验证来更好地进行评估

from sklearn.model_selection import cross_val_score
scores = cross_val_score(tree_reg, housing_prepared, housing_labels, scoring="neg_mean_squared_error", cv=10)
tree_rmse_scores = np.sqrt(-scores)

def display_scores(scores):
print("Scores:", scores)
print("Mean:", scores.mean())
print("Standard deviation:", scores.std())
#display_scores(tree_rmse_scores)
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计算一下线性回归模型的评分

lin_scores = cross_val_score(lin_reg, housing_prepared, housing_labels, scoring="neg_mean_squared_error", cv=10)
lin_rmse_scores = np.sqrt(-lin_scores)
#display_scores(lin_rmse_scores)
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随机森林模型RandomForestRegressor

from sklearn.ensemble import RandomForestRegressor
forest_reg = RandomForestRegressor(n_estimators=10, random_state=42)
forest_reg.fit(housing_prepared, housing_labels)
housing_predictions = forest_reg.predict(housing_prepared)
forest_mse = mean_squared_error(housing_labels, housing_predictions)
forest_rmse = np.sqrt(forest_mse)
#print(forest_rmse)
from sklearn.model_selection import cross_val_score
forest_scores = cross_val_score(forest_reg, housing_prepared, housing_labels, scoring="neg_mean_squared_error", cv=10)
forest_rmse_scores = np.sqrt(-forest_scores)
#display_scores(forest_rmse_scores)
scores = cross_val_score(lin_reg, housing_prepared, housing_labels, scoring="neg_mean_squared_error", cv=10)
#print(pd.Series(np.sqrt(-scores)).describe())
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微调模型

网格搜索

#你可以用Scikit-Learn的GridSearchCV来替你进行探索。你所要做的只是告诉它你要进行实验的超参数是什么，以及需要尝试的值，它将会使用交叉验证来评估超参数值的所有可能的组合。
#下面这段代码搜索RandomForestRegressor的超参数值的最佳组合:
#当你不知道超参数应该赋什么值时，一个简单的方法是连续尝试10的幂次方
from sklearn.ensemble import RandomForestRegressor
from sklearn.model_selection import GridSearchCV
param_grid = [
    {'n_estimators': [3, 10, 30], 'max_features': [2, 4, 6, 8]}, # try 12 (3×4) combinations of hyperparameters
    {'bootstrap': [False], 'n_estimators': [3, 10], 'max_features': [2, 3, 4]}, # then try 6 (2×3) combinations with bootstrap set as False
]
forest_reg = RandomForestRegressor()
grid_search = GridSearchCV(forest_reg, param_grid, cv=5, scoring='neg_mean_squared_error')
grid_search.fit(housing_prepared, housing_labels)
#print(grid_search.best_params_)
#print(grid_search.best_estimator_)

cvres = grid_search.cv_results_
for mean_score, params in zip(cvres["mean_test_score"], cvres["params"]):
   print(np.sqrt(-mean_score), params)
print(pd.DataFrame(grid_search.cv_results_))
#随机搜索
#集成方法

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分析最佳模型及其错误

feature_importances = grid_search.best_estimator_.feature_importances_
#print(feature_importances)
#将这些重要性分数显示在对应的属性名称旁边：
extra_attribs = ["rooms_per_hhold", "pop_per_hhold", "bedrooms_per_room"]
#cat_encoder = cat_pipeline.named_steps["cat_encoder"] # old solution
cat_encoder = full_pipeline.named_transformers_["cat"]
cat_one_hot_attribs = list(cat_encoder.categories_[0])
attributes = num_attribs + extra_attribs + cat_one_hot_attribs
sorted(zip(feature_importances, attributes), reverse=True)
#print(sorted(zip(feature_importances, attributes), reverse=True))
#通过测试集评估系统
from sklearn.metrics import mean_squared_error
final_model = grid_search.best_estimator_
X_test = strat_test_set.drop("median_house_value", axis=1)
y_test = strat_test_set["median_house_value"].copy()
X_test_prepared = full_pipeline.transform(X_test)
final_predictions = final_model.predict(X_test_prepared)
final_mse = mean_squared_error(y_test, final_predictions)
final_rmse = np.sqrt(final_mse)
#print(final_rmse)
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启动、监控和维护系统