Sets or retrieves the "units" attribute of an object.
For units.default replaces the builtin
version, which only works for time series objects. If the variable is
also given a label, subsetting (using [.labelled) will
retain the "units" attribute. For a Surv object,
units first looks for an overall "units" attribute, then
it looks for units for the time2 variable then for time1.
value to which to set result if no appropriate attribute is
found
Value
the units attribute of x, if any; otherwise, the units attribute of
the tspar attribute of x if any; otherwise the value
none. Handling for Surv objects is different (see above).