data.table with columns time and duration.Creates a data.table with columns time and duration,
in which the column time corresponds to the (unique) times in the
input table. In the output, the most recent time given a duration of 1, the
second most recent time given a duration of 2, and so on.
times_and_durations(d)A data.table containing at least a column time, which
is sortable. For example, could be POSIXct dates.
A new data.table, containing columns time (key column)
and duration.