一、Missing Values
1.set up
import pandas as pd
from sklearn.model_selection import train_test_split
# Read the data
X_full = pd.read_csv('../input/train.csv', index_col='Id')
X_test_full = pd.read_csv('../input/test.csv', index_col='Id')
# Remove rows with missing target, separate target from predictors
X_full.dropna(axis=0, subset=['SalePrice'], inplace=True)
y = X_full.SalePrice
X_full.drop(['SalePrice'], axis=1, inplace=True)
# To keep things simple, we'll use only numerical predictors
X = X_full.select_dtypes(exclude=['object'])
X_test = X_test_full.select_dtypes(exclude=['object'])
# Break off validation set from training data
X_train, X_valid, y_train, y_valid = train_test_split(X, y, train_size=0.8, test_size=0.2,
random_state=0)
2.Preliminary investigation
# Shape of training data (num_rows, num_columns)
print(X_train.shape)
# Number of missing values in each column of training data
missing_val_count_by_column = (X_train.isnull().sum())
print(missing_val_count_by_column[missing_val_count_by_column > 0])
from sklearn.ensemble import RandomForestRegressor
from sklearn.metrics import mean_absolute_error
# Function for comparing different approaches
def score_dataset(X_train, X_valid, y_train, y_valid):
model = RandomForestRegressor(n_estimators=100, random_state=0)
model.fit(X_train, y_train)
preds = model.predict(X_valid)
return mean_absolute_error(y_valid, preds)
3.Drop columns with missing values
# Fill in the line below: get names of columns with missing values
cols_with_missing = [col for col in X_train.columns if X_train[col].isnull().any()] # Your code here
# Fill in the lines below: drop columns in training and validation data
reduced_X_train = X_train.drop(cols_with_missing, axis=1)
reduced_X_valid = X_valid.drop(cols_with_missing, axis=1)
print("MAE (Drop columns with missing values):")
print(score_dataset(reduced_X_train, reduced_X_valid, y_train, y_valid))
4.Imputation
from sklearn.impute import SimpleImputer
# Fill in the lines below: imputation
my_imputer = SimpleImputer()
imputed_X_train = pd.DataFrame(my_imputer.fit_transform(X_train))
imputed_X_valid = pd.DataFrame(my_imputer.transform(X_valid))
# Fill in the lines below: imputation removed column names; put them back
imputed_X_train.columns = X_train.columns
imputed_X_valid.columns = X_valid.columns
print("MAE (Imputation):")
print(score_dataset(imputed_X_train, imputed_X_valid, y_train, y_valid))
或者：
# Preprocessed training and validation features
# Imputation
final_imputer = SimpleImputer(strategy='median')
final_X_train = pd.DataFrame(final_imputer.fit_transform(X_train))
final_X_valid = pd.DataFrame(final_imputer.transform(X_valid))
# Imputation removed column names; put them back
final_X_train.columns = X_train.columns
final_X_valid.columns = X_valid.columns
5.Fit the model
# Define and fit model
model = RandomForestRegressor(n_estimators=100, random_state=0)
model.fit(final_X_train, y_train)
# Get validation predictions and MAE
preds_valid = model.predict(final_X_valid)
print("MAE (Your approach):")
print(mean_absolute_error(y_valid, preds_valid))
# Fill in the line below: preprocess test data
final_X_test = pd.DataFrame(final_imputer.transform(X_test))
# Fill in the line below: get test predictions
preds_test = model.predict(final_X_test)
二、categorical-variables
-
set up
同上 -
評價指標
from sklearn.ensemble import RandomForestRegressor
from sklearn.metrics import mean_absolute_error
# function for comparing different approaches
def score_dataset(X_train, X_valid, y_train, y_valid):
model = RandomForestRegressor(n_estimators=100, random_state=0)
model.fit(X_train, y_train)
preds = model.predict(X_valid)
return mean_absolute_error(y_valid, preds)
- Drop columns with categorical data
# Fill in the lines below: drop columns in training and validation data
drop_X_train = X_train.select_dtypes(exclude=['object'])
drop_X_valid = X_valid.select_dtypes(exclude=['object'])
print("MAE from Approach 1 (Drop categorical variables):")
print(score_dataset(drop_X_train, drop_X_valid, y_train, y_valid))
- Label encoding
##########首先刪除有問題的分類列
# All categorical columns
object_cols = [col for col in X_train.columns if X_train[col].dtype == "object"]
# Columns that can be safely label encoded
good_label_cols = [col for col in object_cols if
set(X_train[col]) == set(X_valid[col])]
# Problematic columns that will be dropped from the dataset
bad_label_cols = list(set(object_cols)-set(good_label_cols))
#################然後對沒問題的列進行編碼
from sklearn.preprocessing import LabelEncoder
# Drop categorical columns that will not be encoded
label_X_train = X_train.drop(bad_label_cols, axis=1)
label_X_valid = X_valid.drop(bad_label_cols, axis=1)
# Apply label encoder
label_encoder = LabelEncoder()
for col in set(good_label_cols):
label_X_train[col] = label_encoder.fit_transform(X_train[col])
label_X_valid[col] = label_encoder.transform(X_valid[col])
#################評價
print("MAE from Approach 2 (Label Encoding):")
print(score_dataset(label_X_train, label_X_valid, y_train, y_valid))
- One-hot encoding（只用於少於15種類別）
###################首先刪除多於10種類別的列
# Columns that will be one-hot encoded
low_cardinality_cols = [col for col in object_cols if X_train[col].nunique() < 10]
# Columns that will be dropped from the dataset
high_cardinality_cols = list(set(object_cols)-set(low_cardinality_cols))
print('Categorical columns that will be one-hot encoded:', low_cardinality_cols)
print('\nCategorical columns that will be dropped from the dataset:', high_cardinality_cols)
####################進行one_hot編碼
from sklearn.preprocessing import OneHotEncoder
# Apply one-hot encoder to each column with categorical data
OH_encoder = OneHotEncoder(handle_unknown='ignore', sparse=False)
OH_cols_train = pd.DataFrame(OH_encoder.fit_transform(X_train[low_cardinality_cols]))
OH_cols_valid = pd.DataFrame(OH_encoder.transform(X_valid[low_cardinality_cols]))
# One-hot encoding removed index行索引; put it back
OH_cols_train.index = X_train.index
OH_cols_valid.index = X_valid.index
# Remove categorical columns (will replace with one-hot encoding)
num_X_train = X_train.drop(object_cols, axis=1)
num_X_valid = X_valid.drop(object_cols, axis=1)
# Add one-hot encoded columns to numerical features
OH_X_train = pd.concat([num_X_train, OH_cols_train], axis=1)
OH_X_valid = pd.concat([num_X_valid, OH_cols_valid], axis=1)
三、Pipelines
- set up
import pandas as pd
from sklearn.model_selection import train_test_split
# Read the data
X_full = pd.read_csv('../input/train.csv', index_col='Id')
X_test_full = pd.read_csv('../input/test.csv', index_col='Id')
# Remove rows with missing target, separate target from predictors
X_full.dropna(axis=0, subset=['SalePrice'], inplace=True)
y = X_full.SalePrice
X_full.drop(['SalePrice'], axis=1, inplace=True)
# Break off validation set from training data
X_train_full, X_valid_full, y_train, y_valid = train_test_split(X_full, y,
train_size=0.8, test_size=0.2,
random_state=0)
# "Cardinality" means the number of unique values in a column
# Select categorical columns with relatively low cardinality (convenient but arbitrary)
categorical_cols = [cname for cname in X_train_full.columns if
X_train_full[cname].nunique() < 10 and
X_train_full[cname].dtype == "object"]
# Select numerical columns
numerical_cols = [cname for cname in X_train_full.columns if
X_train_full[cname].dtype in ['int64', 'float64']]
# Keep selected columns only
my_cols = categorical_cols + numerical_cols
X_train = X_train_full[my_cols].copy()
X_valid = X_valid_full[my_cols].copy()
X_test = X_test_full[my_cols].copy()
- Create and Evaluate the Pipeline
from sklearn.compose import ColumnTransformer
from sklearn.pipeline import Pipeline
from sklearn.impute import SimpleImputer
from sklearn.preprocessing import OneHotEncoder
from sklearn.ensemble import RandomForestRegressor
from sklearn.metrics import mean_absolute_error
# Preprocessing for numerical data
numerical_transformer = SimpleImputer(strategy='median')
# Preprocessing for categorical data
categorical_transformer = Pipeline(steps=[
('imputer', SimpleImputer(strategy='most_frequent')),
('onehot', OneHotEncoder(handle_unknown='ignore'))
])
# Bundle preprocessing for numerical and categorical data
preprocessor = ColumnTransformer(
transformers=[
('num', numerical_transformer, numerical_cols),
('cat', categorical_transformer, categorical_cols)
])
# Define model
model = RandomForestRegressor(n_estimators=150, random_state=0)
- 進行預測
# Bundle preprocessing and modeling code in a pipeline
my_pipeline = Pipeline(steps=[('preprocessor', preprocessor),
('model', model)
])
# Preprocessing of training data, fit model
my_pipeline.fit(X_train, y_train)
# Preprocessing of validation data, get predictions
preds = my_pipeline.predict(X_valid)
# Evaluate the model
score = mean_absolute_error(y_valid, preds)
print('MAE:', score)
四、交叉驗證
from sklearn.model_selection import cross_val_score
# Multiply by -1 since sklearn calculates *negative* MAE
scores = -1 * cross_val_score(my_pipeline, X, y,
cv=5,
scoring='neg_mean_absolute_error')
print("MAE scores:\n", scores)
If you’d like to learn more about hyperparameter optimization, you’re encouraged to start with grid search, which is a straightforward method for determining the best combination of parameters for a machine learning model. Thankfully, scikit-learn also contains a built-in function GridSearchCV() that can make your grid search code very efficient!
五、XGBoost
from xgboost import XGBRegressor
# Define the model
my_model = XGBRegressor(n_estimators=1000, learning_rate=0.05)
# Fit the model
# 將數據集轉換一下格式，eval_set的作用是指明沒加入一個新樹，用什麼數據來訓練它
# early_stopping_rounds : 指定當添加樹loss變化不大這個狀態持續的輪數，達到這個數就退出訓練過程
#eval_metric :指定這個衡量的標準，我們選用的是loss。
#verbose ： 這個用來顯示這個loss的結果。如果設置成False則不會輸出每一步的結果
my_model.fit(X_train, y_train,
early_stopping_rounds=5,
eval_set=[(X_valid, y_valid)], eval_metric="logloss"
verbose=False)
# Get predictions
predictions = my_model.predict(X_valid) # Your code here
# Calculate MAE
mae = mean_absolute_error(predictions,y_valid) # Your code here
# Uncomment to print MAE
print("Mean Absolute Error:" , mae_2)