python数据框正则表达式怎么去除元
import pandas as pd
import numpy as np
pd.set_option('display.unicode.east_asian_width', True)
df = pd.DataFrame({'姓名':['张强','李小强','牛新','牛增强','张强','张强发'],
'收入':['500元','530元','470元','600元',np.nan,'560元']})
df=df.dropna(axis=0)
print(df)