在R中按组将上一行添加到相应的列

一个解决方案 dplyr 和 rleid 从…起 data.table :

library(dplyr)

df %>% 
  mutate(id2 = data.table::rleid(id)) %>% 
  group_by(id2) %>% 
  mutate(group2 = lead(group))

# A tibble: 8 x 4
# Groups:   id2 [3]
     id group   id2 group2
  <dbl> <fct> <int> <fct> 
1  1.00 a         1 b     
2  1.00 b         1 c     
3  1.00 c         1 d     
4  1.00 d         1 NA    
5  2.00 a         2 b     
6  2.00 b         2 NA    
7  1.00 c         3 d     
8  1.00 d         3 NA    

如果我理解并更正您的问题,您可以使用以下功能:

id <- c(1,1,1,1,2,2,1,1)
group <- c("a","b","c","d","a","b","c","d")
df <- data.frame(id, group)

add_group2 <- function(df) {
  n <-length(group)
  group2 <- as.character(df$group[2:n])
  group2 <- c(group2, "-")
  group2[which(c(df$id[-n] - c(df$id[2:n]), 0) != 0)] <- "-"
  return(data.frame(df, group2))
}
add_group2(df)

结果应为:

 id group group2
1  1     a      b
2  1     b      c
3  1     c      d
4  1     d      -
5  2     a      b
6  2     b      -
7  1     c      d
8  1     d      -