Used when the true series is not appropriate, as when a forecast is desired and the series is required beyond the original series.
dr2index(index, d1, r1, ...)index with dates extended until the last supported date. The final rate
supplied is the rate for all dates after the final date.
An index (i.e. a data.table with columns date and value,
where date is an arithmetic sequence of monthly, quarterly, or annual dates),
and value is the indexed value for that date.
A single date or value representing a date.
The desired rate of increase for the index from the last date in index
to the end of d1. For example, d1 = 2025 and r1 = 0 applied
to a monthly index would keep value constant until 2025-12-01.
A set of date-rate pairs.