r - 如何分组并仅回填某些组

Question

给定如下面板数据集:

df <- structure(list(date = c(1999L, 2000L, 2001L, 1999L, 2000L, 2001L, 
1999L, 2000L, 2001L), firms = c("A", "A", "A", "B", "B", "B", 
"C", "C", "C"), return = c(5L, NA, 6L, 9L, NA, 10L, 8L, NA, 3L
)), class = "data.frame", row.names = c(NA, -9L))

我可以使用 df %>% group_by(firms) %>% fill(return, .direction= “向上”):

   date firms return
  <int> <chr>  <int>
1  1999 A          5
2  2000 A          6
3  2001 A          6
4  1999 B          9
5  2000 B         10
6  2001 B         10
7  1999 C          8
8  2000 C          3
9  2001 C          3

但我想知道如何回填某些组，即 B 和 C？

预期结果:

  date firms return
1 1999     A      5
2 2000     A     NA
3 2001     A      6
4 1999     B      9
5 2000     B     10
6 2001     B     10
7 1999     C      8
8 2000     C      3
9 2001     C      3

Answer 1

这是一个简单直观的解决方案:

library(data.table)
df %>% group_by(firms) %>% 
mutate(return = ifelse(firms %in% c("B", "C"), nafill(return, type ="locf"), return))

>
  date firms return
1 1999     A      5
2 2000     A     NA
3 2001     A      6
4 1999     B      9
5 2000     B      9
6 2001     B     10
7 1999     C      8
8 2000     C      8
9 2001     C      3
>