One-hot 编码多级列数据

我有以下数据框，其中包含有关不同主题的特征的记录：

ID   Feature
-------------------------
1    A
1    B
2    A
1    A
3    B
3    B
1    C
2    C
3    D

我想获得另一个（聚合的？）数据帧，其中每一行代表一个特定主题，并且有所有单热编码功能的详尽列表：

ID   FEATURE_A FEATURE_B FEATURE_C FEATURE D
--------------------------------------------
1    1         1         1         0
2    1         0         1         0
3    0         1         0         0

如何用Python（Pandas）实现它？

奖励：如何实现一个版本，其中特征列包含出现次数，而不仅仅是二进制标志？

Use join http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.join.html with get_dummies http://pandas.pydata.org/pandas-docs/stable/generated/pandas.get_dummies.html, then groupby http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.groupby.html并聚合max:

df =df[['ID']].join(pd.get_dummies(df['Feature']).add_prefix('FEATURE_')).groupby('ID').max()
print (df)
    FEATURE_A  FEATURE_B  FEATURE_C  FEATURE_D
ID                                            
1           1          1          1          0
2           1          0          1          0
3           0          1          0          1

Detail:

print (pd.get_dummies(df['Feature']))
   A  B  C  D
0  1  0  0  0
1  0  1  0  0
2  1  0  0  0
3  1  0  0  0
4  0  1  0  0
5  0  1  0  0
6  0  0  1  0
7  0  0  1  0
8  0  0  0  1

另一种解决方案是多标签二值化器 http://scikit-learn.org/stable/modules/generated/sklearn.preprocessing.MultiLabelBinarizer.html and DataFrame构造函数：

from sklearn.preprocessing import MultiLabelBinarizer

mlb = MultiLabelBinarizer()
df1 = pd.DataFrame(mlb.fit_transform(df['Feature']),
                   columns=['FEATURE_' + x for x in mlb.classes_], 
                   index=df.ID).max(level=0)
print (df1)
    FEATURE_A  FEATURE_B  FEATURE_C  FEATURE_D
ID                                            
1           1          1          1          0
2           1          0          1          0
3           0          1          0          1

Timings:

np.random.seed(123)
N = 100000
L = list('abcdefghijklmno'.upper()) 
df = pd.DataFrame({'Feature': np.random.choice(L, N),
                   'ID':np.random.randint(10000,size=N)})

def jez(df):
    mlb = MultiLabelBinarizer()
    return pd.DataFrame(mlb.fit_transform(df['Feature']),
                   columns=['FEATURE_' + x for x in mlb.classes_], 
                   index=df.ID).max(level=0)


#jez1
In [464]: %timeit (df[['ID']].join(pd.get_dummies(df['Feature']).add_prefix('FEATURE_')).groupby('ID').max())
10 loops, best of 3: 39.3 ms per loop

In [465]: %timeit (jez(df))
10 loops, best of 3: 138 ms per loop

#Scott Boston1
In [466]: %timeit (df.set_index('ID')['Feature'].str.get_dummies().add_prefix('FEATURE_').max(level=0))
1 loop, best of 3: 1.03 s per loop

#wen1
In [467]: %timeit (pd.crosstab(df.ID,df.Feature).gt(0).astype(int).add_prefix('FEATURE '))
1 loop, best of 3: 383 ms per loop

#wen2
In [468]: %timeit (pd.get_dummies(df.drop_duplicates().set_index('ID')).sum(level=0))
10 loops, best of 3: 47 ms per loop

Caveat