根据前n行有条件地创建新列

Question

我有一个如下设置的数据框：

 df <- data.frame("id" = c(111,111,111,222,222,222,222,333,333,333,333), "Location" = c("A","B","A","A","C","B","A","B","A","A","A"), "Encounter" = c(1,2,3,1,2,3,4,1,2,3,4))

      id Location Encounter
1  111        A         1
2  111        B         2
3  111        A         3
4  222        A         1
5  222        C         2
6  222        B         3
7  222        A         4
8  333        B         1
9  333        A         2
10 333        B         3
11 333        A         4

我基本上是试图为每个id组在先前的Encounter中创建一个位置的二进制标志。因此它看起来像：

    id Location Encounter Flag
1  111        A         1    0
2  111        B         2    0
3  111        A         3    1
4  222        A         1    0
5  222        C         2    0
6  222        B         3    0
7  222        A         4    1
8  333        B         1    0
9  333        A         2    0
10 333        B         3    1
11 333        A         4    1

我试图弄清楚如何执行if语句，例如：

df$Flag <- case_when((df$id - lag(df$id)) == 0 ~ case_when(df$Location == lag(df$Location, 1)  
                                                           | df$Location == lag(df$Location, 2) 
                                                           | df$Location == lag(df$Location, 3) ~ 1, T ~ 0), T ~ 0)

    id Location Flag
1  111        A    0
2  111        B    0
3  111        A    1
4  222        A    0
5  222        C    0
6  222        B    0
7  222        A    1
8  333        B    0
9  333        A    1
10 333        B    1
11 333        A    1

但是这会给第9行错误地分配1，并且在实际数据中遇到15次以上的情况，因此变得非常麻烦。我希望找到一种方法来完成

lag(df$Location, 1:df$Encounter)

但是我知道lag（）需要k的整数，因此特定命令将不起作用。

任何帮助将不胜感激！

也是这里的第一次发布者，请随时对以后的问题提出建设性的批评！ :)

Answer 1

使用data.table：

library(data.table)
df <- data.table("id" = c(111,111,111,222,222,222,222,333,333,333,333), "Location" = c("A","B","A","A","C","B","A","B","A","A","A"), "Encounter" = c(1,2,3,1,2,3,4,1,2,3,4))
df[, flag:=1]
df[, flag:=cumsum(flag), by=.(id,Location)]
df[, flag:=ifelse(flag>1,1,0)]