logical. If TRUE a leading zero will be added to
values from 0 up to 1.
digits
The number of digits to use. Defaults to 2. Can be set
globally via: options(numformdigits = n) where n is the number of
digits beyond the decimal point to include.
p
A string to paste at the beginning of the output from f_num.
Defaults to dollar sign. This could be useful, for example, to turn a
single dolar sign into an escaped version for LaTeX output.