R 创建创建标签或类别的新列，直到它到达新标签

这是我的数据框

df2 <- structure(list(Code = c("ICB-9_label_1", "1", "2", "3", 
"4", "5", "1", "ICB-10_label_2", "3", "4", "5", 
"1", "2", "3", "3", "5", "1", "2", 
"3", "4", "5", "1", "2", "3", "4", 
"5", "1", "2", "3", "4", "5", "1", 
"2", "3", "4", "5", "1", "2", "3", 
"4", "5", "1", "2", "3", "4", "5", 
"1"), Description = c("description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here", "description here", "description here", "description here", 
"description here")), row.names = c(NA, -47L), class = c("tbl_df", 
"tbl", "data.frame"))

这是一张桌子的样子:

 Code             Description
ICB-9_label_1     description here          
1                 description here          
2                 description here          
3                 description here          
4                 description here          
5                 description here          
1                 description here          
ICB-10_label_2    description here          
3                 description here          
4                 description here

我想创建第三列"标签".它会一直显示"ICB\u 9\u label\u 1"，直到它找到"ICB\u 10\u label\u 2"的行号，然后该列会一直显示"ICB\u 10\u label\u 2".我不想覆盖第一列中的数字，因为1、2、3、4、5值很重要.