Get counts and proportions by group(s)

group_prop.R

group_prop <- function(df, ...) {
  # enquo the dots
  vars <- enquos(...)
  
  # count then calculate
  # proportions
  df_count <- df %>%
    count(!!!vars)
  
  if (length(vars) > 1) {
    df_count %>%
      group_by(!!vars[[1]]) %>%
      mutate(prop = n / sum(n),
             prop_se = sqrt(prop * (1 - prop) / sum(n))) %>%
      ungroup()
  } else {
    df_count %>%
      mutate(prop = n / sum(n),
             prop_se = sqrt(prop * (1 - prop) / sum(n))) %>%
      ungroup()
  }
} 

Updated to divide by the total sample size rather than the number in each category for the prop_se. See e.g. https://stats.stackexchange.com/questions/396952/standard-error-of-individual-groups-in-a-multinomial-distribution