dataframe中如何用平均值替换相应列的缺失值？

df = pd.read_csv('https://raw.githubusercontent.com/selva86/datasets/master/Cars93_miss.csv',nrows=10)
print(df[['Min.Price','Max.Price']].head())
# 平均值替换缺失值
df_out = df[['Min.Price', 'Max.Price']] = df[['Min.Price', 'Max.Price']].apply(lambda x: x.fillna(x.mean()))
print(df_out.head())

#>	   Min.Price  Max.Price
	0       12.9       18.8
	1       29.2       38.7
	2       25.9       32.3
	3        NaN       44.6
	4        NaN        NaN

#>	   Min.Price  Max.Price
	0       12.9       18.8
	1       29.2       38.7
	2       25.9       32.3
	3       23.0       44.6
	4       23.0       29.9