broom boostrap() function using groups

bootstrap_groups.R

bootstrap <- function (df, m, block = FALSE)  {
  n <- nrow(df)
  attr(df, "indices") <-
  if (is(df, "grouped_df") && length(attr(df, "indices")) && block) {
    replicate(m, 
              unlist(lapply(attr(df, "indices"), 
                            function(x) sample(length(x), replace = TRUE)),
                     recursive = FALSE, use.names = FALSE),
              simplify = FALSE)
  } else {
     replicate(m, sample(n, replace = TRUE) - 
                                       1, simplify = FALSE)
  }
  attr(df, "drop") <- TRUE
  attr(df, "group_sizes") <- rep(n, m)
  attr(df, "biggest_group_size") <- n
  attr(df, "labels") <- data.frame(replicate = 1:m)
  attr(df, "vars") <- list(quote(replicate))
  class(df) <- c("grouped_df", "tbl_df", "tbl", "data.frame")
  df
}