pandas怎么去除nan_删除python pandas中的NaN值

数据是来自人口普查数据的成年人收入，行看起来像：31, Private, 84154, Some-college, 10, Married-civ-spouse, Sales, Husband, White, Male, 0, 0, 38, NaN, >50K

48, Self-emp-not-inc, 265477, Assoc-acdm, 12, Married-civ-spouse, Prof-specialty, Husband, White, Male, 0, 0, 40, United-States, <=50K

我正在尝试从pandas中的CSV文件加载的数据帧中删除所有带有NaNs的行。>>> import pandas as pd

>>> income = pd.read_csv('income.data')

>>> income['type'].unique()

array([ State-gov, Self-emp-not-inc, Private, Federal-gov, Local-gov,

NaN, Self-emp-inc, Without-pay, Never-worked], dtype=object)

>>> income.dropna(how='any') # should drop all rows with NaNs

>>> income['type'].unique()

array([ State-gov, Self-emp-not-inc, Private, Federal-gov, Local-gov,

NaN, Self-emp-inc, Without-pay, Never-worked], dtype=object)

Self-emp-inc, nan], dtype=object) # what??

>>> income = income.dropna(how='any') # ok, maybe reassignment will work?

>>> income['type'].unique()

array([ State-gov, Self-emp-not-inc, Private, Federal-gov, Local-gov,

NaN, Self-emp-inc, Without-pay, Never-worked], dtype=object) # what??

我试着用更小的example.csv：label,age,sex

1,43,M

-1,NaN,F

1,65,NaN

而且dropna()在这里对分类和数值的nan都很有效。怎么回事？我对熊猫还不熟悉，只是在学绳子。