Time Sequence Class
This class is a compact representation of a
time/date vector in an arithemetic sequence.
The timeSequence class extends the positionsCalendar class.
Valid timeSequence objects must contain a single non-NA value in
at least three of the from, to, by, and length slots.
If all four are present, the length
slot is ignored, and a warning message is generated when
the sequence is used. If length is present and not being ignored, it must
be non-negative (that is, a zero-length sequence is equivalent to timeDate()).
Otherwise, to have a valid sequence, adding by to from must go
towards to. The default sequence (generated by calling timeSequence() or
new("timeSequence")) has length 0.
A timeSequence can be coerced to timeDate using as,
and regularly-spaced times/dates (or time/date vectors spaced
by regular numbers of months) can be coerced to timeSequence
using as. This fails if the input is not a regular
sequence within a tolerance given by timeDateOptions("ts.eps").
Most operations that work for timeDate objects also work on timeSequence
objects (for example, mathematical functions, arithmetic,
comparison operators, and subscripting) by first coercing to a time/date
vector. Therefore they do not return timeSequence objects. Because
of this, it is more efficient to coerce a timeSequence
to timeDate using as before performing an extended set of
calculations on the original object, rather than coercing
for each operation.
(timeDate) the start of the sequence.
(timeDate) the end of the sequence.
(timeInterval) the increment for the sequence.
(integer) the length of the sequence.
(event) time periods to remove from the sequence.
(positionsCalendar) times/dates to add to the sequence.
(character) the time/date output format for sequence display.
(character) the time zone for the sequence.