我处于初学者到中级数据科学水平。我想使用knn.
由于数据帧包含字符串和floats，我需要使用 对值进行编码/解码LabelEncoder。
我的方法如下：
- 替换 NaN 以便能够编码
- 编码文本值并将它们放入字典中
- 检索要使用 knn 估算的 NaN（先前转换的）
- 用 knn 赋值
- 解码字典中的值
不幸的是，在最后一步中，估算值会添加无法解码的新值（unseen labels错误消息）。
你能向我解释我做错了什么吗？理想情况下请帮我纠正它。在结束之前，我想说我知道还有其他类似的工具OneHotEncoder，但我不太了解它们，我发现 LabelEncoder 更直观，因为你可以直接在数据框中看到它（其中LabelEncoder提供了一个数组）。
请在下面找到我的方法示例，非常感谢您的帮助：
[1]
# Import libraries.
import pandas as pd
import numpy as np
# intialise data of lists.
data = {'Name':['Jack', np.nan, 'Victoria', 'Nicolas', 'Victor', 'Brad'], 'Age':[59, np.nan, 29, np.nan, 65, 50], 'Car color':['Blue', 'Black', np.nan, 'Black', 'Grey', np.nan], 'Height ':[177, 150, np.nan, 180, 175, 190]}
# Make a DataFrame
df = pd.DataFrame(data)
# Print the output.
df
Output :
Name Age Car color Height
0 Jack 59.0 Blue 177.0
1 NaN NaN Black 150.0
2 Victoria 29.0 NaN NaN
3 Nicolas NaN Black 180.0
4 Victor 65.0 Grey 175.0
5 Brad 50.0 NaN 190.0
[2]
# LabelEncoder does not work with NaN values, so I replace them with value '1000' :
df = df.replace(np.nan, 1000)
# And to avoid errors, str columns must be set as strings (even '1000' value) :
df[['Name','Car color']] = df[['Name','Car color']].astype(str)
df
Output
Name Age Car color Height
0 Jack 59.0 Blue 177.0
1 1000 1000.0 Black 150.0
2 Victoria 29.0 1000 1000.0
3 Nicolas 1000.0 Black 180.0
4 Victor 65.0 Grey 175.0
5 Brad 50.0 1000 190.0
[3]
# Import LabelEncoder library :
from sklearn.preprocessing import LabelEncoder
# define labelencoder :
le = LabelEncoder()
# Import defaultdict library to make a dict of labelencoder :
from collections import defaultdict
# Initiate a dict of LabelEncoder values :
encoder_dict = defaultdict(LabelEncoder)
# Make a new dataframe of LabelEncoder values :
df[['Name','Car color']] = df[['Name','Car color']].apply(lambda x: encoder_dict[x.name].fit_transform(x))
# Show output :
df
Output
Name Age Car color Height
0 2 59.0 2 177.0
1 0 1000.0 1 150.0
2 5 29.0 0 1000.0
3 3 1000.0 1 180.0
4 4 65.0 3 175.0
5 1 50.0 0 190.0
[4]
#Reverse back 1000 to missing values in order to impute them :
df = df.replace(1000, np.nan)
df
Output
Name Age Car color Height
0 2 59.0 2 177.0
1 0 NaN 1 150.0
2 5 29.0 0 NaN
3 3 NaN 1 180.0
4 4 65.0 3 175.0
5 1 50.0 0 190.0
[5]
# Import knn imputer library to replace impute missing values :
from sklearn.impute import KNNImputer
# Define imputer :
imputer = KNNImputer(n_neighbors=2)
# impute and reassign index/colonnes :
df = pd.DataFrame(np.round(imputer.fit_transform(df)),columns = df.columns)
df
Output
Name Age Car color Height
0 2.0 59.0 2.0 177.0
1 0.0 47.0 1.0 150.0
2 5.0 29.0 0.0 165.0
3 3.0 44.0 1.0 180.0
4 4.0 65.0 3.0 175.0
5 1.0 50.0 0.0 190.0
[6]
# Decode data :
inverse_transform_lambda = lambda x: encoder_dict[x.name].inverse_transform(x)
# Apply it to df -> THIS IS WHERE ERROR OCCURS :
df[['Name','Car color']].apply(inverse_transform_lambda)
错误信息 ：
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
<ipython-input-55-8a5e369215f6> in <module>()
----> 1 df[['Name','Car color']].apply(inverse_transform_lambda)
5 frames
/usr/local/lib/python3.6/dist-packages/pandas/core/frame.py in apply(self, func, axis, broadcast, raw, reduce, result_type, args, **kwds)
6926 kwds=kwds,
6927 )
-> 6928 return op.get_result()
6929
6930 def applymap(self, func):
/usr/local/lib/python3.6/dist-packages/pandas/core/apply.py in get_result(self)
184 return self.apply_raw()
185
--> 186 return self.apply_standard()
187
188 def apply_empty_result(self):
/usr/local/lib/python3.6/dist-packages/pandas/core/apply.py in apply_standard(self)
290
291 # compute the result using the series generator
--> 292 self.apply_series_generator()
293
294 # wrap results
/usr/local/lib/python3.6/dist-packages/pandas/core/apply.py in apply_series_generator(self)
319 try:
320 for i, v in enumerate(series_gen):
--> 321 results[i] = self.f(v)
322 keys.append(v.name)
323 except Exception as e:
<ipython-input-54-f16f4965b2c4> in <lambda>(x)
----> 1 inverse_transform_lambda = lambda x: encoder_dict[x.name].inverse_transform(x)
/usr/local/lib/python3.6/dist-packages/sklearn/preprocessing/_label.py in inverse_transform(self, y)
297 "y contains previously unseen labels: %s" % str(diff))
298 y = np.asarray(y)
--> 299 return self.classes_[y]
300
301 def _more_tags(self):
IndexError: ('arrays used as indices must be of integer (or boolean) type', 'occurred at index Name')