트레인, 테스트 세트로 분리할 때 사용 하는 모듈
80 : 20으로 나누기.
from sklearn.model_selection import train_test_split
train, test = train_test_split(df, train_size=0.80, test_size=0.20,
stratify=df['target'], random_state=2)
X_train, y_train, X_test, y_test = train.drop('target', axis = 1), train.target, test.drop('target', axis = 1), test.target
X_train.shape, y_train.shape, X_test.shape, y_test.shape