Convert the units of a units
object to their base units, as defined by
the udunits database (SI units).
Examples
x <- set_units(32, mJ/g)
convert_to_base(x)
#> 32 [J/kg]
convert_to_base(x, keep_fraction=FALSE)
#> 32 [Gy]
convert_to_base(x, simplify=FALSE)
#> 32 [m^2*kg/(s^2*kg)]
convert_to_base(x, simplify=FALSE, keep_fraction=FALSE)
#> 32 [m^2/s^2]