python-熊猫：读取列中带有特殊字符的文件

在我拥有的数据中,一些特征值是？.如何用NA代替它们？

编辑

代码和输出如下：

df = pd.read_csv("cca-census-income.csv", header = None)

df.replace('?', np.nan, inplace=True)

df.ix[0,]

23                Other relative of householder
24                                      1700.09
25                                            ?
26                                            ?
27                                            ?
28             Not in universe under 1 year old
29                                            ?
30                                            0

解决方法:

添加参数na_values =’？’到read_csv.

样品：

import pandas as pd
import io


temp=u"""Date Time,a
2010-01-27 16:00:00,?
2010-01-27 16:10:00,2.2
2010-01-27 16:30:00,1.7"""

df = pd.read_csv(io.StringIO(temp),na_values='?')
print (df)
             Date Time    a
0  2010-01-27 16:00:00  NaN
1  2010-01-27 16:10:00  2.2
2  2010-01-27 16:30:00  1.7

编辑：

谢谢‘shivsn’的建议,添加skipinitialspace = True：

temp=u"""Date Time,a
 ? , ?
? ,?
2010-01-27 16:30:00,1.7"""

df = pd.read_csv(io.StringIO(temp),na_values=['?', '? '], skipinitialspace =True)
print (df)
             Date Time    a
0                  NaN  NaN
1                  NaN  NaN
2  2010-01-27 16:30:00  1.7

EDIT1按文件：

似乎前面没有空格？：

df = pd.read_csv('census-income.data', 
                 header = None, 
                 na_values=['?'], 
                 skipinitialspace =True)
print (df)