使用因子列将级别列添加到数据框

Question

我有以下df玩具示例：

    structure(list(a = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("1", 
"2", "3"), class = "factor"), b = c("ku", "pu", "dd", "ka", "la", 
"gu", "kuku", "pupu", "d", "a", "su", "mo", "kui", "pue", "vwe", 
"rr", "wq", "q", "ppr", "tr", "qs", "cf")), .Names = c("a", "b"
), row.names = c(NA, -22L), class = c("tbl_df", "tbl", "data.frame"
))

我想将a转换为因子对象，并将其级别填充到其他列中（级别1对应于1，2到2等）

请告知如何添加此附加因子水平列？

所需的输出应为：

a   b     a_lev
1   k      1
1   v      1
1   fs     1 
1   fdf    1
2   fe     2
3   ee     3
2   ere    2 
1   rre    1 
2   rerere 2 
3   rer    3
2   ere    2
1   fd     1
1   fd     1

Answer 1

我们提取列的levels，然后通过与元素匹配来展开

df$a_lev <- levels(df$a)[df$a]

class将是character，因此，使用as.character会更容易

df$a_lev <- as.character(df$a)