I need to select `n` cells below the matched column sequence. Let's assume `n = 2` and the specific column sequence is A, B and C. After this sequence, I would like to pick up two more cells below this sequence. My table is:

```
Table1 <- data.frame(ID=rep(c(1 ,2  ,3  ,4  ,5  ,6  ,7  ,8  ,9  ,10 ,11 ,12 ,13 ,14 ,15 ,16 ,17 ,18 ,19 ,20 ,21 ,22 ,23 ,24 ,25 ,26 ,27 ,28 ,29 ,30 ,31)), Sequence=rep(c("A",  "B",    "D",    "E",    "A",    "B",    "C",    "f",    "n",    "p",    "C",    "D",    "D",    "E",    "A",    "B",    "C",    "z",    "t",    "g",    "A",    "C",    "D",    "A",    "B",    "C",    "p",    "l",    "x",    "v",    "A")))

```

I like to have this Table:

```
Table2 <- data.frame(ID=rep(c(1 ,2  ,3  ,4  ,5  ,6  ,7  ,8  ,9  ,10 ,11 ,12 ,13 ,14 ,15 ,16 ,17 ,18 ,19 ,20 ,21 ,22 ,23 ,24 ,25 ,26 ,27 ,28 ,29 ,30 ,31)), Sequence=rep(c("A",  "B",    "D",    "E",    "A",    "B",    "C",    "f",    "n",    "p",    "C",    "D",    "D",    "E",    "A",    "B",    "C",    "z",    "t",    "g",    "A",    "C",    "D",    "A",    "B",    "C",    "p",    "l",    "x",    "v",    "A")), Selected=rep(c("",   "", "", "", "A",    "B",    "C",    "f",    "n",    "", "", "", "", "", "A",    "B",    "C",    "z",    "t",    "", "", "", "", "A",    "B",    "C",    "p",    "l",    "", "", "")))

```

Can you please help me with this?