具体用法详情请看：https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.mask.html，
现在主要说一下区别:
where 是条件为False才替换，而mask是条件为True才替换
import pandas as pd s = pd.Series(range(5)) ‘‘‘ 0 0 1 1 2 2 3 3 4 4 dtype: int64 ‘‘‘ s.where(s>1) ‘‘‘ 0 NaN 1 NaN 2 2.0 3 3.0 4 4.0 dtype: float64 ‘‘‘ s.mask(s>1) ‘‘‘ 0 0.0 1 1.0 2 NaN 3 NaN 4 NaN dtype: float64 ‘‘‘ s.where(s>1,10) ‘‘‘ 0 10 1 10 2 2 3 3 4 4 dtype: int64 ‘‘‘ s.mask(s>1,10) ‘‘‘ 0 0 1 1 2 10 3 10 4 10 dtype: int64 ‘‘‘
原文：https://www.cnblogs.com/cgmcoding/p/13589693.html