Sample groups in a tidy data frame.

sample_groups.R

sample_groups <- function(.data, ..., n, prop) {
  slice_size <- dplyr:::check_slice_size(n, prop)
  .data %>% 
    dplyr::group_by(...) %>% 
    tidyr::nest() %>% 
    dplyr::ungroup() %>% 
    {
      if (slice_size$type == "n") {
        dplyr::slice_sample(., n=slice_size$n)
      } else {
        dplyr::slice_sample(., prop=slice_size$prop)
      }
    } %>%
    tidyr::unnest(data)
}

This function samples from groups of a dataframe. It groups by the grouping columns, samples groups, and then ungroups. The number of groups can be specified as either a number or a proportion, similar to dplyr::slice_sample.