这是dataFrame的代码

导入numpy作为np导入panda作为pd

Data_Frame1 = {
  "company": ["A","B","C","A","A","B","C","B","C"],
  "employee": [10,12,13,10,51,11,12,12,12],
  "salary":[2,"unknown",4,"unknown",5,"unknown",8,8,4],
  "compartment":["madhyapradesh","uttarpradesh","gujarat","madhyapradesh","uttarpradesh","uttarpradesh","gujarat","gujarat","madhyapradesh"]
} 
df_1 = pd.DataFrame(Data_Frame1)
df_1

其输出类似于This is dataframe
对于mode，我编写了如下代码

emp=df_1.groupby('company')[['employee','salary',"compartment"]].agg(lambda x: pd.Series.mode(x)[0])
emp

它的输出是这样的

The output of above code

此处我将空值替换为unknow，在此公司中，B有三个值对应于salary列，如[“unknown'，“unknown”，8]，但由于它采用mode，因此将unknown作为结果，但我希望它将8作为mode，因为此处我将空值替换为unknown。那么实现此功能的代码应该是什么