2.5 데이터_전처리(데이터 인코딩, 피처스케일링과 정규화) (실습)

1  데이터 인코딩

2  레이블 인코딩(Label encoding)

 

from sklearn.preprocessing import LabelEncoder

items = ['TV','냉장고','전자렌지','컴퓨터','선풍기','선풍기','믹서','믹서']

# LabelEncoder 클래스를 encoder 객체로 생성한 후
encoder = LabelEncoder()

# fit은 transform 수행 전 틀을 맞춰주는 역할
encoder.fit(items)

# encoder.transform( ) 으로 label 인코딩 수행. 
labels = encoder.transform(items)
print('인코딩 변환값:', labels)

>>> 인코딩 변환값: [0 1 4 5 3 3 2 2]

 

print('인코딩 클래스:', encoder.classes_)
>>> 인코딩 클래스: ['TV' '냉장고' '믹서' '선풍기' '전자렌지' '컴퓨터']

 

print('디코딩 원본 값:', encoder.inverse_transform([0, 1, 4, 5, 3, 3, 2, 2]))

>>> 디코딩 원본 값: ['TV' '냉장고' '전자렌지' '컴퓨터' '선풍기' '선풍기' '믹서' '믹서']

 

3  원-핫 인코딩(One-Hot encoding)

3.1  (1) sklearn에서의 원핫 인코딩

<sklearn에서의 원핫 인코딩은 좀 복잡하다>
첫번째, 먼저 숫자값으로 변환을 위해 LabelEncoder로 변환합니다. 
두번째, 2차원 데이터로 변환합니다. (reshape 활용)
세번째, 원-핫 인코딩을 적용합니다. 

 

 

from sklearn.preprocessing import OneHotEncoder
import numpy as np

items=['TV','냉장고','전자렌지','컴퓨터','선풍기','선풍기','믹서','믹서']

# 첫번째, 먼저 숫자값으로 변환을 위해 LabelEncoder로 변환합니다. 
encoder = LabelEncoder()
encoder.fit(items)
labels = encoder.transform(items)
labels


>>> 
array([0, 1, 4, 5, 3, 3, 2, 2])

 

# 두번째, 2차원 데이터로 변환합니다. 
labels = labels.reshape(-1, 1)
labels

>>> 

array([[0],
       [1],
       [4],
       [5],
       [3],
       [3],
       [2],
       [2]])

 

# 마지막으로 원-핫 인코딩을 적용합니다.
oh_encoder = OneHotEncoder()
oh_encoder.fit(labels)
oh_labels = oh_encoder.transform(labels)

print('원-핫 인코딩 데이터')
print(oh_labels.shape)
oh_labels.toarray()

>>>
원-핫 인코딩 데이터
(8, 6)
array([[1., 0., 0., 0., 0., 0.],
       [0., 1., 0., 0., 0., 0.],
       [0., 0., 0., 0., 1., 0.],
       [0., 0., 0., 0., 0., 1.],
       [0., 0., 0., 1., 0., 0.],
       [0., 0., 0., 1., 0., 0.],
       [0., 0., 1., 0., 0., 0.],
       [0., 0., 1., 0., 0., 0.]])

 

3.2  (2) 판다스의 원핫 인코딩

판다스의 get_dummies 함수를 이용하면 쉽게 원핫 인코딩이 가능하다

 

import pandas as pd

df = pd.DataFrame({'item':['TV','냉장고','전자렌지','컴퓨터','선풍기','선풍기','믹서','믹서'] })
df

 

 

pd.get_dummies(df)

 

 

 

 

4  피처 스케일링과 정규화

4.1  (1) StandardScaler

 

from sklearn.datasets import load_iris
import pandas as pd

 

# 붓꽃 데이터 셋을 로딩하고 DataFrame으로 변환합니다. 
iris = load_iris()
iris_data = iris.data

 

iris_data

array([[5.1, 3.5, 1.4, 0.2],
       [4.9, 3. , 1.4, 0.2],
       [4.7, 3.2, 1.3, 0.2],
       [4.6, 3.1, 1.5, 0.2],
       [5. , 3.6, 1.4, 0.2],
       [5.4, 3.9, 1.7, 0.4],
       [4.6, 3.4, 1.4, 0.3],
       [5. , 3.4, 1.5, 0.2],
       [4.4, 2.9, 1.4, 0.2],
       [4.9, 3.1, 1.5, 0.1],
       [5.4, 3.7, 1.5, 0.2],
       [4.8, 3.4, 1.6, 0.2],
       [4.8, 3. , 1.4, 0.1],
       [4.3, 3. , 1.1, 0.1],
       [5.8, 4. , 1.2, 0.2],
       [5.7, 4.4, 1.5, 0.4],
       [5.4, 3.9, 1.3, 0.4],
       [5.1, 3.5, 1.4, 0.3],
       [5.7, 3.8, 1.7, 0.3],
       [5.1, 3.8, 1.5, 0.3],
       [5.4, 3.4, 1.7, 0.2],
       [5.1, 3.7, 1.5, 0.4],
       [4.6, 3.6, 1. , 0.2],
       [5.1, 3.3, 1.7, 0.5],
       [4.8, 3.4, 1.9, 0.2],
       [5. , 3. , 1.6, 0.2],
       [5. , 3.4, 1.6, 0.4],
       [5.2, 3.5, 1.5, 0.2],
       [5.2, 3.4, 1.4, 0.2],
       [4.7, 3.2, 1.6, 0.2],
       [4.8, 3.1, 1.6, 0.2],
       [5.4, 3.4, 1.5, 0.4],
       [5.2, 4.1, 1.5, 0.1],
       [5.5, 4.2, 1.4, 0.2],
       [4.9, 3.1, 1.5, 0.2],
       [5. , 3.2, 1.2, 0.2],
       [5.5, 3.5, 1.3, 0.2],
       [4.9, 3.6, 1.4, 0.1],
       [4.4, 3. , 1.3, 0.2],
       [5.1, 3.4, 1.5, 0.2],
       [5. , 3.5, 1.3, 0.3],
       [4.5, 2.3, 1.3, 0.3],
       [4.4, 3.2, 1.3, 0.2],
       [5. , 3.5, 1.6, 0.6],
       [5.1, 3.8, 1.9, 0.4],
       [4.8, 3. , 1.4, 0.3],
       [5.1, 3.8, 1.6, 0.2],
       [4.6, 3.2, 1.4, 0.2],
       [5.3, 3.7, 1.5, 0.2],
       [5. , 3.3, 1.4, 0.2],
       [7. , 3.2, 4.7, 1.4],
       [6.4, 3.2, 4.5, 1.5],
       [6.9, 3.1, 4.9, 1.5],
       [5.5, 2.3, 4. , 1.3],
       [6.5, 2.8, 4.6, 1.5],
       [5.7, 2.8, 4.5, 1.3],
       [6.3, 3.3, 4.7, 1.6],
       [4.9, 2.4, 3.3, 1. ],
       [6.6, 2.9, 4.6, 1.3],
       [5.2, 2.7, 3.9, 1.4],
       [5. , 2. , 3.5, 1. ],
       [5.9, 3. , 4.2, 1.5],
       [6. , 2.2, 4. , 1. ],
       [6.1, 2.9, 4.7, 1.4],
       [5.6, 2.9, 3.6, 1.3],
       [6.7, 3.1, 4.4, 1.4],
       [5.6, 3. , 4.5, 1.5],
       [5.8, 2.7, 4.1, 1. ],
       [6.2, 2.2, 4.5, 1.5],
       [5.6, 2.5, 3.9, 1.1],
       [5.9, 3.2, 4.8, 1.8],
       [6.1, 2.8, 4. , 1.3],
       [6.3, 2.5, 4.9, 1.5],
       [6.1, 2.8, 4.7, 1.2],
       [6.4, 2.9, 4.3, 1.3],
       [6.6, 3. , 4.4, 1.4],
       [6.8, 2.8, 4.8, 1.4],
       [6.7, 3. , 5. , 1.7],
       [6. , 2.9, 4.5, 1.5],
       [5.7, 2.6, 3.5, 1. ],
       [5.5, 2.4, 3.8, 1.1],
       [5.5, 2.4, 3.7, 1. ],
       [5.8, 2.7, 3.9, 1.2],
       [6. , 2.7, 5.1, 1.6],
       [5.4, 3. , 4.5, 1.5],
       [6. , 3.4, 4.5, 1.6],
       [6.7, 3.1, 4.7, 1.5],
       [6.3, 2.3, 4.4, 1.3],
       [5.6, 3. , 4.1, 1.3],
       [5.5, 2.5, 4. , 1.3],
       [5.5, 2.6, 4.4, 1.2],
       [6.1, 3. , 4.6, 1.4],
       [5.8, 2.6, 4. , 1.2],
       [5. , 2.3, 3.3, 1. ],
       [5.6, 2.7, 4.2, 1.3],
       [5.7, 3. , 4.2, 1.2],
       [5.7, 2.9, 4.2, 1.3],
       [6.2, 2.9, 4.3, 1.3],
       [5.1, 2.5, 3. , 1.1],
       [5.7, 2.8, 4.1, 1.3],
       [6.3, 3.3, 6. , 2.5],
       [5.8, 2.7, 5.1, 1.9],
       [7.1, 3. , 5.9, 2.1],
       [6.3, 2.9, 5.6, 1.8],
       [6.5, 3. , 5.8, 2.2],
       [7.6, 3. , 6.6, 2.1],
       [4.9, 2.5, 4.5, 1.7],
       [7.3, 2.9, 6.3, 1.8],
       [6.7, 2.5, 5.8, 1.8],
       [7.2, 3.6, 6.1, 2.5],
       [6.5, 3.2, 5.1, 2. ],
       [6.4, 2.7, 5.3, 1.9],
       [6.8, 3. , 5.5, 2.1],
       [5.7, 2.5, 5. , 2. ],
       [5.8, 2.8, 5.1, 2.4],
       [6.4, 3.2, 5.3, 2.3],
       [6.5, 3. , 5.5, 1.8],
       [7.7, 3.8, 6.7, 2.2],
       [7.7, 2.6, 6.9, 2.3],
       [6. , 2.2, 5. , 1.5],
       [6.9, 3.2, 5.7, 2.3],
       [5.6, 2.8, 4.9, 2. ],
       [7.7, 2.8, 6.7, 2. ],
       [6.3, 2.7, 4.9, 1.8],
       [6.7, 3.3, 5.7, 2.1],
       [7.2, 3.2, 6. , 1.8],
       [6.2, 2.8, 4.8, 1.8],
       [6.1, 3. , 4.9, 1.8],
       [6.4, 2.8, 5.6, 2.1],
       [7.2, 3. , 5.8, 1.6],
       [7.4, 2.8, 6.1, 1.9],
       [7.9, 3.8, 6.4, 2. ],
       [6.4, 2.8, 5.6, 2.2],
       [6.3, 2.8, 5.1, 1.5],
       [6.1, 2.6, 5.6, 1.4],
       [7.7, 3. , 6.1, 2.3],
       [6.3, 3.4, 5.6, 2.4],
       [6.4, 3.1, 5.5, 1.8],
       [6. , 3. , 4.8, 1.8],
       [6.9, 3.1, 5.4, 2.1],
       [6.7, 3.1, 5.6, 2.4],
       [6.9, 3.1, 5.1, 2.3],
       [5.8, 2.7, 5.1, 1.9],
       [6.8, 3.2, 5.9, 2.3],
       [6.7, 3.3, 5.7, 2.5],
       [6.7, 3. , 5.2, 2.3],
       [6.3, 2.5, 5. , 1.9],
       [6.5, 3. , 5.2, 2. ],
       [6.2, 3.4, 5.4, 2.3],
       [5.9, 3. , 5.1, 1.8]])

 

iris.feature_names

>>>
['sepal length (cm)',
 'sepal width (cm)',
 'petal length (cm)',
 'petal width (cm)']

 

iris_df = pd.DataFrame(data=iris_data, columns=iris.feature_names)

print('feature 들의 평균 값')
print(iris_df.mean(), '\n')

print('feature 들의 분산 값')
print(iris_df.var())

>>>
feature 들의 평균 값
sepal length (cm)    5.843333
sepal width (cm)     3.057333
petal length (cm)    3.758000
petal width (cm)     1.199333
dtype: float64 

feature 들의 분산 값
sepal length (cm)    0.685694
sepal width (cm)     0.189979
petal length (cm)    3.116278
petal width (cm)     0.581006
dtype: float64

 

 

from sklearn.preprocessing import StandardScaler

# StandardScaler객체 생성
scaler = StandardScaler()

# StandardScaler 로 데이터 셋 변환. fit( ) 과 transform( ) 호출.  
scaler.fit(iris_df)
iris_scaled = scaler.transform(iris_df)
iris_scaled

array([[-9.00681170e-01,  1.01900435e+00, -1.34022653e+00,
        -1.31544430e+00],
       [-1.14301691e+00, -1.31979479e-01, -1.34022653e+00,
        -1.31544430e+00],
       [-1.38535265e+00,  3.28414053e-01, -1.39706395e+00,
        -1.31544430e+00],
       [-1.50652052e+00,  9.82172869e-02, -1.28338910e+00,
        -1.31544430e+00],
       [-1.02184904e+00,  1.24920112e+00, -1.34022653e+00,
        -1.31544430e+00],
       [-5.37177559e-01,  1.93979142e+00, -1.16971425e+00,
        -1.05217993e+00],
       [-1.50652052e+00,  7.88807586e-01, -1.34022653e+00,
        -1.18381211e+00],
       [-1.02184904e+00,  7.88807586e-01, -1.28338910e+00,
        -1.31544430e+00],
       [-1.74885626e+00, -3.62176246e-01, -1.34022653e+00,
        -1.31544430e+00],
       [-1.14301691e+00,  9.82172869e-02, -1.28338910e+00,
        -1.44707648e+00],
       [-5.37177559e-01,  1.47939788e+00, -1.28338910e+00,
        -1.31544430e+00],
       [-1.26418478e+00,  7.88807586e-01, -1.22655167e+00,
        -1.31544430e+00],
       [-1.26418478e+00, -1.31979479e-01, -1.34022653e+00,
        -1.44707648e+00],
       [-1.87002413e+00, -1.31979479e-01, -1.51073881e+00,
        -1.44707648e+00],
       [-5.25060772e-02,  2.16998818e+00, -1.45390138e+00,
        -1.31544430e+00],
       [-1.73673948e-01,  3.09077525e+00, -1.28338910e+00,
        -1.05217993e+00],
       [-5.37177559e-01,  1.93979142e+00, -1.39706395e+00,
        -1.05217993e+00],
       [-9.00681170e-01,  1.01900435e+00, -1.34022653e+00,
        -1.18381211e+00],
       [-1.73673948e-01,  1.70959465e+00, -1.16971425e+00,
        -1.18381211e+00],
       [-9.00681170e-01,  1.70959465e+00, -1.28338910e+00,
        -1.18381211e+00],
       [-5.37177559e-01,  7.88807586e-01, -1.16971425e+00,
        -1.31544430e+00],
       [-9.00681170e-01,  1.47939788e+00, -1.28338910e+00,
        -1.05217993e+00],
       [-1.50652052e+00,  1.24920112e+00, -1.56757623e+00,
        -1.31544430e+00],
       [-9.00681170e-01,  5.58610819e-01, -1.16971425e+00,
        -9.20547742e-01],
       [-1.26418478e+00,  7.88807586e-01, -1.05603939e+00,
        -1.31544430e+00],
       [-1.02184904e+00, -1.31979479e-01, -1.22655167e+00,
        -1.31544430e+00],
       [-1.02184904e+00,  7.88807586e-01, -1.22655167e+00,
        -1.05217993e+00],
       [-7.79513300e-01,  1.01900435e+00, -1.28338910e+00,
        -1.31544430e+00],
       [-7.79513300e-01,  7.88807586e-01, -1.34022653e+00,
        -1.31544430e+00],
       [-1.38535265e+00,  3.28414053e-01, -1.22655167e+00,
        -1.31544430e+00],
       [-1.26418478e+00,  9.82172869e-02, -1.22655167e+00,
        -1.31544430e+00],
       [-5.37177559e-01,  7.88807586e-01, -1.28338910e+00,
        -1.05217993e+00],
       [-7.79513300e-01,  2.40018495e+00, -1.28338910e+00,
        -1.44707648e+00],
       [-4.16009689e-01,  2.63038172e+00, -1.34022653e+00,
        -1.31544430e+00],
       [-1.14301691e+00,  9.82172869e-02, -1.28338910e+00,
        -1.31544430e+00],
       [-1.02184904e+00,  3.28414053e-01, -1.45390138e+00,
        -1.31544430e+00],
       [-4.16009689e-01,  1.01900435e+00, -1.39706395e+00,
        -1.31544430e+00],
       [-1.14301691e+00,  1.24920112e+00, -1.34022653e+00,
        -1.44707648e+00],
       [-1.74885626e+00, -1.31979479e-01, -1.39706395e+00,
        -1.31544430e+00],
       [-9.00681170e-01,  7.88807586e-01, -1.28338910e+00,
        -1.31544430e+00],
       [-1.02184904e+00,  1.01900435e+00, -1.39706395e+00,
        -1.18381211e+00],
       [-1.62768839e+00, -1.74335684e+00, -1.39706395e+00,
        -1.18381211e+00],
       [-1.74885626e+00,  3.28414053e-01, -1.39706395e+00,
        -1.31544430e+00],
       [-1.02184904e+00,  1.01900435e+00, -1.22655167e+00,
        -7.88915558e-01],
       [-9.00681170e-01,  1.70959465e+00, -1.05603939e+00,
        -1.05217993e+00],
       [-1.26418478e+00, -1.31979479e-01, -1.34022653e+00,
        -1.18381211e+00],
       [-9.00681170e-01,  1.70959465e+00, -1.22655167e+00,
        -1.31544430e+00],
       [-1.50652052e+00,  3.28414053e-01, -1.34022653e+00,
        -1.31544430e+00],
       [-6.58345429e-01,  1.47939788e+00, -1.28338910e+00,
        -1.31544430e+00],
       [-1.02184904e+00,  5.58610819e-01, -1.34022653e+00,
        -1.31544430e+00],
       [ 1.40150837e+00,  3.28414053e-01,  5.35408562e-01,
         2.64141916e-01],
       [ 6.74501145e-01,  3.28414053e-01,  4.21733708e-01,
         3.95774101e-01],
       [ 1.28034050e+00,  9.82172869e-02,  6.49083415e-01,
         3.95774101e-01],
       [-4.16009689e-01, -1.74335684e+00,  1.37546573e-01,
         1.32509732e-01],
       [ 7.95669016e-01, -5.92373012e-01,  4.78571135e-01,
         3.95774101e-01],
       [-1.73673948e-01, -5.92373012e-01,  4.21733708e-01,
         1.32509732e-01],
       [ 5.53333275e-01,  5.58610819e-01,  5.35408562e-01,
         5.27406285e-01],
       [-1.14301691e+00, -1.51316008e+00, -2.60315415e-01,
        -2.62386821e-01],
       [ 9.16836886e-01, -3.62176246e-01,  4.78571135e-01,
         1.32509732e-01],
       [-7.79513300e-01, -8.22569778e-01,  8.07091462e-02,
         2.64141916e-01],
       [-1.02184904e+00, -2.43394714e+00, -1.46640561e-01,
        -2.62386821e-01],
       [ 6.86617933e-02, -1.31979479e-01,  2.51221427e-01,
         3.95774101e-01],
       [ 1.89829664e-01, -1.97355361e+00,  1.37546573e-01,
        -2.62386821e-01],
       [ 3.10997534e-01, -3.62176246e-01,  5.35408562e-01,
         2.64141916e-01],
       [-2.94841818e-01, -3.62176246e-01, -8.98031345e-02,
         1.32509732e-01],
       [ 1.03800476e+00,  9.82172869e-02,  3.64896281e-01,
         2.64141916e-01],
       [-2.94841818e-01, -1.31979479e-01,  4.21733708e-01,
         3.95774101e-01],
       [-5.25060772e-02, -8.22569778e-01,  1.94384000e-01,
        -2.62386821e-01],
       [ 4.32165405e-01, -1.97355361e+00,  4.21733708e-01,
         3.95774101e-01],
       [-2.94841818e-01, -1.28296331e+00,  8.07091462e-02,
        -1.30754636e-01],
       [ 6.86617933e-02,  3.28414053e-01,  5.92245988e-01,
         7.90670654e-01],
       [ 3.10997534e-01, -5.92373012e-01,  1.37546573e-01,
         1.32509732e-01],
       [ 5.53333275e-01, -1.28296331e+00,  6.49083415e-01,
         3.95774101e-01],
       [ 3.10997534e-01, -5.92373012e-01,  5.35408562e-01,
         8.77547895e-04],
       [ 6.74501145e-01, -3.62176246e-01,  3.08058854e-01,
         1.32509732e-01],
       [ 9.16836886e-01, -1.31979479e-01,  3.64896281e-01,
         2.64141916e-01],
       [ 1.15917263e+00, -5.92373012e-01,  5.92245988e-01,
         2.64141916e-01],
       [ 1.03800476e+00, -1.31979479e-01,  7.05920842e-01,
         6.59038469e-01],
       [ 1.89829664e-01, -3.62176246e-01,  4.21733708e-01,
         3.95774101e-01],
       [-1.73673948e-01, -1.05276654e+00, -1.46640561e-01,
        -2.62386821e-01],
       [-4.16009689e-01, -1.51316008e+00,  2.38717193e-02,
        -1.30754636e-01],
       [-4.16009689e-01, -1.51316008e+00, -3.29657076e-02,
        -2.62386821e-01],
       [-5.25060772e-02, -8.22569778e-01,  8.07091462e-02,
         8.77547895e-04],
       [ 1.89829664e-01, -8.22569778e-01,  7.62758269e-01,
         5.27406285e-01],
       [-5.37177559e-01, -1.31979479e-01,  4.21733708e-01,
         3.95774101e-01],
       [ 1.89829664e-01,  7.88807586e-01,  4.21733708e-01,
         5.27406285e-01],
       [ 1.03800476e+00,  9.82172869e-02,  5.35408562e-01,
         3.95774101e-01],
       [ 5.53333275e-01, -1.74335684e+00,  3.64896281e-01,
         1.32509732e-01],
       [-2.94841818e-01, -1.31979479e-01,  1.94384000e-01,
         1.32509732e-01],
       [-4.16009689e-01, -1.28296331e+00,  1.37546573e-01,
         1.32509732e-01],
       [-4.16009689e-01, -1.05276654e+00,  3.64896281e-01,
         8.77547895e-04],
       [ 3.10997534e-01, -1.31979479e-01,  4.78571135e-01,
         2.64141916e-01],
       [-5.25060772e-02, -1.05276654e+00,  1.37546573e-01,
         8.77547895e-04],
       [-1.02184904e+00, -1.74335684e+00, -2.60315415e-01,
        -2.62386821e-01],
       [-2.94841818e-01, -8.22569778e-01,  2.51221427e-01,
         1.32509732e-01],
       [-1.73673948e-01, -1.31979479e-01,  2.51221427e-01,
         8.77547895e-04],
       [-1.73673948e-01, -3.62176246e-01,  2.51221427e-01,
         1.32509732e-01],
       [ 4.32165405e-01, -3.62176246e-01,  3.08058854e-01,
         1.32509732e-01],
       [-9.00681170e-01, -1.28296331e+00, -4.30827696e-01,
        -1.30754636e-01],
       [-1.73673948e-01, -5.92373012e-01,  1.94384000e-01,
         1.32509732e-01],
       [ 5.53333275e-01,  5.58610819e-01,  1.27429511e+00,
         1.71209594e+00],
       [-5.25060772e-02, -8.22569778e-01,  7.62758269e-01,
         9.22302838e-01],
       [ 1.52267624e+00, -1.31979479e-01,  1.21745768e+00,
         1.18556721e+00],
       [ 5.53333275e-01, -3.62176246e-01,  1.04694540e+00,
         7.90670654e-01],
       [ 7.95669016e-01, -1.31979479e-01,  1.16062026e+00,
         1.31719939e+00],
       [ 2.12851559e+00, -1.31979479e-01,  1.61531967e+00,
         1.18556721e+00],
       [-1.14301691e+00, -1.28296331e+00,  4.21733708e-01,
         6.59038469e-01],
       [ 1.76501198e+00, -3.62176246e-01,  1.44480739e+00,
         7.90670654e-01],
       [ 1.03800476e+00, -1.28296331e+00,  1.16062026e+00,
         7.90670654e-01],
       [ 1.64384411e+00,  1.24920112e+00,  1.33113254e+00,
         1.71209594e+00],
       [ 7.95669016e-01,  3.28414053e-01,  7.62758269e-01,
         1.05393502e+00],
       [ 6.74501145e-01, -8.22569778e-01,  8.76433123e-01,
         9.22302838e-01],
       [ 1.15917263e+00, -1.31979479e-01,  9.90107977e-01,
         1.18556721e+00],
       [-1.73673948e-01, -1.28296331e+00,  7.05920842e-01,
         1.05393502e+00],
       [-5.25060772e-02, -5.92373012e-01,  7.62758269e-01,
         1.58046376e+00],
       [ 6.74501145e-01,  3.28414053e-01,  8.76433123e-01,
         1.44883158e+00],
       [ 7.95669016e-01, -1.31979479e-01,  9.90107977e-01,
         7.90670654e-01],
       [ 2.24968346e+00,  1.70959465e+00,  1.67215710e+00,
         1.31719939e+00],
       [ 2.24968346e+00, -1.05276654e+00,  1.78583195e+00,
         1.44883158e+00],
       [ 1.89829664e-01, -1.97355361e+00,  7.05920842e-01,
         3.95774101e-01],
       [ 1.28034050e+00,  3.28414053e-01,  1.10378283e+00,
         1.44883158e+00],
       [-2.94841818e-01, -5.92373012e-01,  6.49083415e-01,
         1.05393502e+00],
       [ 2.24968346e+00, -5.92373012e-01,  1.67215710e+00,
         1.05393502e+00],
       [ 5.53333275e-01, -8.22569778e-01,  6.49083415e-01,
         7.90670654e-01],
       [ 1.03800476e+00,  5.58610819e-01,  1.10378283e+00,
         1.18556721e+00],
       [ 1.64384411e+00,  3.28414053e-01,  1.27429511e+00,
         7.90670654e-01],
       [ 4.32165405e-01, -5.92373012e-01,  5.92245988e-01,
         7.90670654e-01],
       [ 3.10997534e-01, -1.31979479e-01,  6.49083415e-01,
         7.90670654e-01],
       [ 6.74501145e-01, -5.92373012e-01,  1.04694540e+00,
         1.18556721e+00],
       [ 1.64384411e+00, -1.31979479e-01,  1.16062026e+00,
         5.27406285e-01],
       [ 1.88617985e+00, -5.92373012e-01,  1.33113254e+00,
         9.22302838e-01],
       [ 2.49201920e+00,  1.70959465e+00,  1.50164482e+00,
         1.05393502e+00],
       [ 6.74501145e-01, -5.92373012e-01,  1.04694540e+00,
         1.31719939e+00],
       [ 5.53333275e-01, -5.92373012e-01,  7.62758269e-01,
         3.95774101e-01],
       [ 3.10997534e-01, -1.05276654e+00,  1.04694540e+00,
         2.64141916e-01],
       [ 2.24968346e+00, -1.31979479e-01,  1.33113254e+00,
         1.44883158e+00],
       [ 5.53333275e-01,  7.88807586e-01,  1.04694540e+00,
         1.58046376e+00],
       [ 6.74501145e-01,  9.82172869e-02,  9.90107977e-01,
         7.90670654e-01],
       [ 1.89829664e-01, -1.31979479e-01,  5.92245988e-01,
         7.90670654e-01],
       [ 1.28034050e+00,  9.82172869e-02,  9.33270550e-01,
         1.18556721e+00],
       [ 1.03800476e+00,  9.82172869e-02,  1.04694540e+00,
         1.58046376e+00],
       [ 1.28034050e+00,  9.82172869e-02,  7.62758269e-01,
         1.44883158e+00],
       [-5.25060772e-02, -8.22569778e-01,  7.62758269e-01,
         9.22302838e-01],
       [ 1.15917263e+00,  3.28414053e-01,  1.21745768e+00,
         1.44883158e+00],
       [ 1.03800476e+00,  5.58610819e-01,  1.10378283e+00,
         1.71209594e+00],
       [ 1.03800476e+00, -1.31979479e-01,  8.19595696e-01,
         1.44883158e+00],
       [ 5.53333275e-01, -1.28296331e+00,  7.05920842e-01,
         9.22302838e-01],
       [ 7.95669016e-01, -1.31979479e-01,  8.19595696e-01,
         1.05393502e+00],
       [ 4.32165405e-01,  7.88807586e-01,  9.33270550e-01,
         1.44883158e+00],
       [ 6.86617933e-02, -1.31979479e-01,  7.62758269e-01,
         7.90670654e-01]])

 

 

# transform( )시 scale 변환된 데이터 셋이 numpy ndarry로 반환되어 이를 DataFrame으로 변환
iris_df_scaled = pd.DataFrame(data=iris_scaled, columns=iris.feature_names)
iris_df_scaled

 

 

print('feature 들의 평균 값')
print(iris_df_scaled.mean(), '\n')

print('feature 들의 분산 값')
print(iris_df_scaled.var())


>>>
feature 들의 평균 값
sepal length (cm)   -1.690315e-15
sepal width (cm)    -1.842970e-15
petal length (cm)   -1.698641e-15
petal width (cm)    -1.409243e-15
dtype: float64 

feature 들의 분산 값
sepal length (cm)    1.006711
sepal width (cm)     1.006711
petal length (cm)    1.006711
petal width (cm)     1.006711
dtype: float64

 

-> 모든 컬럼 값의 평균은 0에 아주 가까운 값으로, 분산은 1에 가까운 값으로 변환되었다.

 

 

4.2  (2) MinMaxScaler

 

from sklearn.preprocessing import MinMaxScaler

# MinMaxScaler객체 생성
scaler = MinMaxScaler()

# MinMaxScaler 로 데이터 셋 변환. fit() 과 transform() 호출.  
scaler.fit(iris_df)
iris_scaled = scaler.transform(iris_df)

 

# transform()시 scale 변환된 데이터 셋이 numpy ndarry로 반환되어 이를 DataFrame으로 변환
iris_df_scaled = pd.DataFrame(data=iris_scaled, columns=iris.feature_names)

print('feature들의 최소 값')
print(iris_df_scaled.min(), '\n')

print('feature들의 최대 값')
print(iris_df_scaled.max())

>>>
feature들의 최소 값
sepal length (cm)    0.0
sepal width (cm)     0.0
petal length (cm)    0.0
petal width (cm)     0.0
dtype: float64 

feature들의 최대 값
sepal length (cm)    1.0
sepal width (cm)     1.0
petal length (cm)    1.0
petal width (cm)     1.0
dtype: float64

 

모든 피처의 값이 0~1 사이로 변환되었다.

 

-> 표준화, 정규화로 머신러닝을 돌리면, 기존의 데이터와 다른 결과가 나온다.

그 중에서 성능을 비교하여 성능이 잘 나오는 것을 선택하면 된다!