R：根据第一次出现分配组值

Question

我想根据“事件”列中“事故”的第一次出现来分配顺序组值 (1-n)。因此，从开始到第一次事故的所有内容，包括事故本身，都属于第 1 组。同样的原则将适用于下一组。你知道我怎样才能在 R 中实现这一点吗？谢谢！

Answer 1

我们做逻辑表达式的lag，得到累加和

library(dplyr)
df1 %>%
    mutate(Group = cumsum(lag(Events == "Accident", default = TRUE)))
#     Events Group
#1         A     1
#2         A     1
#3         A     1
#4         B     1
#5         C     1
#6         A     1
#7         C     1
#8         B     1
#9  Accident     1
#10        C     2
#11        C     2
#12        C     2
#13        B     2
#14        A     2
#15 Accident     2
#16        C     3
#17        A     3
#18        A     3
#19        B     3
#20        B     3
#21 Accident     3

数据

df1 <- structure(list(Events = c("A", "A", "A", "B", "C", "A", "C", 
"B", "Accident", "C", "C", "C", "B", "A", "Accident", "C", "A", 
 "A", "B", "B", "Accident")), class = "data.frame", row.names = c(NA, 
-21L))