Python 如何使用条件从另一列中提取值？

我想根据另一列中的值创建一列。我发现了这一点，但我认为这是行不通的，因为在“抽象”数据之前，我需要检查所有的“Unique_String”值

我想要什么？

我想通过我的“文本”列“循环”（？），看看是否有可用的数据。如果没有，它应该查看“Unique_String”列，提取（如果可用）值，并将其粘贴到文本列中

数据

Unique_String                 Text 
AAA                           Here is text! 
AAA                           Here is text!
BBB                           Here is text as well!
BBB                           Here is text as well! 
BBB                           Feyenoord
CCC                           nan
CCC                           nan 

我有这样一个数据帧：

Unique_String                 Text 
AAA                           Here is text! 
AAA                           nan
BBB                           nan
BBB                           Here is text as well! 
BBB                           Feyenoord
CCC                           nan
CCC                           nan

所需输出为：

Unique_String                 Text 
AAA                           Here is text! 
AAA                           Here is text!
BBB                           Here is text as well!
BBB                           Here is text as well! 
BBB                           Feyenoord
CCC                           nan
CCC                           nan 

---

非常感谢

这里是每个组的必要的向前和向后填充调用函数：

df['Text'] = df.groupby('Unique_String')['Text'].apply(lambda x: x.ffill().bfill())
print (df)
  Unique_String                   Text
0           AAA          Here is text!
1           AAA          Here is text!
2           BBB  Here is text as well!
3           BBB  Here is text as well!
4           BBB              Feyenoord
5           CCC                    NaN
6           CCC                    NaN

df.groupby（'Unique_String'）['Text'].apply（lambda x:x.ffill（）.bfill（））