實現one hot encode獨熱編碼的兩種方法

實現one hot encode的兩種方法：

https://stackoverflow.com/questions/37292872/how-can-i-one-hot-encode-in-python

• 利用pandas實現one hot encode:

#  transform a given column into one hot. Use prefix to have multiple dummies
>>> import pandas as pd
>>> df = pd.DataFrame({'A': ['a', 'b', 'c'], 'B': ['b', 'a', 'c']})
>>> # Get one hot encoding of columns B
... 
>>> df
   A  B
0  a  b
1  b  a
2  c  c
>>> one_hot = pd.get_dummies(df['B'])
>>> # Drop columns B as it is now encoded
... 
>>> df = df.drop('B', axis=1)
>>> # Join the encoded df
... 
>>> df = df.join(one_hot)
>>> df
   A  a  b  c
0  a  0  1  0
1  b  1  0  0
2  c  0  0  1

• 一個定性特徵啞編碼的demo：

def one_hot(df, cols):
    """
    @param df pandas DataFrame
    @param cols a list of columns to encode 
    @return a DataFrame with one-hot encoding
    """
    for each in cols:
        dummies = pd.get_dummies(df[each], prefix=each, drop_first=False)
        df = pd.concat([df, dummies], axis=1)
    return df

• 使用 sklearn進行特徵變量啞編碼：

>>> from sklearn.preprocessing import OneHotEncoder
>>> enc = OneHotEncoder()
>>> enc.fit([[0, 0, 3], [1,1,0], [0,2,1], [1,0,2]])
OneHotEncoder(categorical_features='all', dtype=<class 'numpy.float64'>,
       handle_unknown='error', n_values='auto', sparse=True)
>>> enc.n_values_
array([2, 3, 4])
>>> enc.feature_indices_
array([0, 2, 5, 9])
>>> enc.transform([[0,1,1]])
<1x9 sparse matrix of type '<class 'numpy.float64'>'
    with 3 stored elements in Compressed Sparse Row format>
>>> enc.transform([[0,1,1]]).toarray()
array([[ 1.,  0.,  0.,  1.,  0.,  0.,  1.,  0.,  0.]])

• 一個保存在全局的Label_Binarizer的demo：

from sklearn.preprocessing import LabelBinarizer 
label_binarizer = LabelBinarizer()
label_binarizer.fit(all_your_labels_list) # need to be global or remembered to use it later

def one_hot_encode(x):
    """
    One hot encode a list of sample labels. Return a one-hot encoded vector for each label.
    : x: List of sample Labels
    : return: Numpy array of one-hot encoded labels
    """
    return label_binarizer.transform(x)