printing of units

[edzer]

We have now

> set_units(1, m/s/kg)
# 1 m/kg/s

but that is against NIST recommendations, see. 6.1.6.

[t-kalinowski]

see #89, in particular, I wonder of offloading this to the C library through ud.format (ut_format) will solve this.

[edzer]

For this case yes:

> units:::R_ut_format(units:::R_ut_parse("m/s/kg"))
[1] "m·kg⁻¹·s⁻¹"

but more in general, e.g.

> units:::R_ut_format(units:::R_ut_parse("mile/gallon"))
[1] "425143.683171079 m⁻²"

we see that udunits brings everything back to a constant and powers on the 7 base units. This is of course correct, but not readable:

• ++ the UTF-8 formatting of multiply and powers (which it also parses)
• -- loss of reference/readability
• -- no control over the precision with which the constant is printed, e.g. in the header of a tibble