Find the repeating interval within a vector of doses

This is intended to find the interval over which x repeats by the rule unique(mod(x, interval)) is minimized.

find.tau(x, na.action = stats::na.omit, options = list(), tau.choices = NULL)

Arguments

x	the vector to find the interval within
na.action	What to do with NAs in `x`
options	List of changes to the default `PKNCA.options` for calculations.
tau.choices	the intervals to look for if the doses are not all equally spaced.

A scalar indicating the repeating interval with the most repetition.

If all values are NA then NA is returned.
If all values are the same, then 0 is returned.
If all values are equally spaced, then that spacing is returned.
If one of the choices can minimize the number of unique values, then that is returned.
If none of the choices can minimize the number of unique values, then -1 is returned.