R: Time ID

time_id {timeplyr}

R Documentation

Time ID

Description

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.

Usage

time_id(
  x,
  time_by = NULL,
  g = NULL,
  na_skip = TRUE,
  time_type = getOption("timeplyr.time_type", "auto"),
  shift = 1L
)

Arguments

`x`	Time variable. Can be a `Date`, `POSIXt`, `numeric`, `integer`, `yearmon`, or `yearqtr`.
`time_by`	Time unit. This signifies the granularity of the time data with which to measure gaps in the sequence. If your data is daily for example, supply `time_by = "days"`. If weekly, supply `time_by = "week"`. Must be one of the three: string, specifying either the unit or the number and unit, e.g `time_by = "days"` or `time_by = "2 weeks"` named list of length one, the unit being the name, and the number the value of the list, e.g. `list("days" = 7)`. For the vectorized time functions, you can supply multiple values, e.g. `list("days" = 1:10)`. Numeric vector. If time_by is a numeric vector and x is not a date/datetime, then arithmetic is used, e.g `time_by = 1`.
`g`	Object used for grouping x. This can for example be a vector or data frame. `g` is passed directly to `collapse::GRP()`.
`na_skip`	Should `NA` values be skipped? Default is `TRUE`.
`time_type`	If "auto", `periods` are used for the time expansion when days, weeks, months or years are specified, and `durations` are used otherwise.
`shift`	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.

Details

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.

Value