Essentially a wrapper to endpoints()
with the appropriate period
specified. The result is the number of endpoints found.
As a compromise between simplicity and accuracy, the results will always
round up to the nearest complete period. Subtract 1 from the result to
get the completed periods.
For finer grain detail one should call the higher frequency functions.
An alternative summary can be found with periodicity(x)
and
unclass(periodicity(x))
.