Aggregate data on time

Typically what I use for aggregating dates for ggplot2 plots - convert date (or POSIX etc) to first day of week

periodise_date <- function(x, period = 'weeks') {
  as.Date(cut.Date(as.Date(x), period))
}

Outline of usage:

overall_trend_data <-
  dat[, .(Cases = .N),
      .(Week = periodise_date(`Notification date`))]
ggplot(overall_trend_data, aes(x = Week, y = Cases)) +
  geom_bar(stat = 'identity') +
	labs(x = 'Notification (week beginning)')