group by gender using a tibble

# group by
# gender, baseline BMI and race
gender <- tibble(
  SEX =c("M","F"),
  SEXN=c(1,2)
)

advs_grouped <- advs_bign %>%
  left_join(gender, by = c("SEX")) %>%
  mutate(
    groupn=SEXN,
    group=SEX
  )