Generate a time ID that signifies how many time steps away a time value is from the starting time point or more intuitively, this is the time passed since the first time point.
time_id(x, timespan = granularity(x), g = NULL, na_skip = TRUE, shift = 1L)An integer vector the same length as x.
Time vector.
E.g. a Date, POSIXt, numeric or any time-based vector.
timespan.
Object used for grouping x.
This can for example be a vector or data frame.
g is passed directly to collapse::GRP().
Should NA values be skipped? Default is TRUE.
Value used to shift the time IDs. Typically this is 1 to ensure the IDs start at 1 but can be 0 or even negative if for example your time values are going backwards in time.
This is heavily inspired by collapse::timeid but differs in 3 ways:
The time steps need not be the greatest common divisor of successive differences
The starting time point may not necessarily
be the earliest chronologically and thus time_id can generate negative IDs.
g can be supplied to calculate IDs by group.
time_id(c(3, 2, 1)) is not the same as collapse::timeid(c(3, 2, 1)).
In general time_id(sort(x))
should be equal to collapse::timeid(sort(x)).
The time difference GCD is always calculated using all the data and not
by-group.
time_elapsed time_seq_id