useUseMethods

skim.data.frame <- function(.data) {
  rows <- purrr::map(.data, skim_v)
  combined <- dplyr::bind_rows(rows, .id = "var")
  return(structure(combined, class = c("skim_df", class(combined))))
}

skim.grouped_df <- function(.data){
  nested_df <- .data %>% 
    tidyr::nest() 
  groups <-  as.character(dplyr::groups(.data))
  group_values <- purrrlyr::by_row(nested_df[, groups], ~dplyr::combine(.))
  
  skim_df <- nested_df %>% 
    dplyr::mutate(stats = purrr::map(data, skim)) %>% 
    dplyr::mutate(stats = purrr::map2(stats, 
                                      group_values$.out,
                                      ~append_group_vars(.x, .y, groups = groups)))
  
  combined <- dplyr::bind_rows(skim_df$stats)
  
}