How to count the cumulative number of subgroupings using dplyr?

Question

I'm trying to run the number of cumulative subgroupings using dplyr, as illustrated and explanation in the image below. I am trying to solve for Flag2 in the image. Any recommendations for how to do this?

Beneath the image I also have the reproducible code that runs all columns up through Flag1 which works fine.

Reproducible code:

library(dplyr)

myData <- 
  data.frame(
    Element = c("A","B","B","B","B","B","A","C","C","C","C","C"),
    Group = c(0,0,1,1,2,2,0,3,3,0,0,0)
  )


excelCopy <- myData %>% 
  group_by(Element) %>% 
  mutate(Element_Count = row_number()) %>% 
  mutate(Flag1 = case_when(Group > 0 ~ match(Group, unique(Group)),TRUE ~ Element_Count)) %>%
  ungroup()
  
print.data.frame(excelCopy)

Answer 1

Using row_number and setting 0 values to NA

library(dplyr)

excelCopy |> 
  group_by(Element, Group) |> 
  mutate(Flag2 = ifelse(Group == 0, NA, row_number()))

 Element Group Element_Count Flag1 Flag2
   <chr>   <dbl>         <int> <int> <int>
 1 A           0             1     1    NA
 2 B           0             1     1    NA
 3 B           1             2     2     1
 4 B           1             3     2     2
 5 B           2             4     3     1
 6 B           2             5     3     2
 7 A           0             2     2    NA
 8 C           3             1     1     1
 9 C           3             2     1     2
10 C           0             3     3    NA
11 C           0             4     4    NA
12 C           0             5     5    NA