I wanted to create a group variable with specific conditions based on the values of GT. If GT is ‘I’, it should generate a different number. If GT is ‘G’, the following rules should apply:

1. For the first four consecutive ‘G’s, assign the same number.
2. If there are five consecutive ‘G’s, assign the same number to the first three ‘G’s and a different number to the remaining two ‘G’s.

My Attempt:

So far I got the following:

library(tidyverse)
df1 <- data.frame(
  GT = c(rep("G", 9), rep("I", 2), rep("G", 2), rep("I", 1))
)
df1
#>    GT
#> 1   G
#> 2   G
#> 3   G
#> 4   G
#> 5   G
#> 6   G
#> 7   G
#> 8   G
#> 9   G
#> 10  I
#> 11  I
#> 12  G
#> 13  G
#> 14  I

# Add the group variable based on the conditions
df1 <- 
  df1 %>%
  mutate(
    group = case_when(
      GT == "I" ~ row_number(),  # Each 'I' gets a unique number
      GT == "G" ~ (cumsum(GT == "G") - 1) %/% 4 + 1  # Group G's in batches of 4
    )
  )

df1
#>    GT group
#> 1   G     1
#> 2   G     1
#> 3   G     1
#> 4   G     1
#> 5   G     2
#> 6   G     2
#> 7   G     2
#> 8   G     2
#> 9   G     3
#> 10  I    10
#> 11  I    11
#> 12  G     3
#> 13  G     3
#> 14  I    14

Required Output

  GT group
1   G     1
2   G     1
3   G     1
4   G     1
5   G     2
6   G     2
7   G     2
8   G     3
9   G     3
10  I    10
11  I    11
12  G     3
13  G     3
14  I    14