r - Identifying the index number in a group of counts -
i have df need tally , group group. want identify index(?) of observation in grouping. the group a has 4 observations, want to attach index of 3 3rd a observation. df %>% group_by(group) %>% mutate(count = n()) # group index count #1 1 4 #2 2 4 #3 3 4 #4 4 4 #5 b 1 1 #6 b 2 1 #7 c 1 3 #8 c 2 3 #9 c 3 3 #10 d 1 1 you want use window function row_number() : df %>% group_by(group) %>% mutate(index = row_number()) # explicit row_number(group)