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Package options

Source: R/options-package.R
chemunits_options.Rd

These options are best set via chemunits_options() and queried via get_chemunits_option(). However, the base functions options() and getOption() work as well but require a chemunits. prefix (the package name and a dot) for the option name. Setting an option to a value of NULL means that the default is used.

Usage

chemunits_options(...)

get_chemunits_option(x)

Arguments

...

set package options, syntax identical to options()

x

name of the option to retrieve

Functions

  • chemunits_options(): set option values

  • get_chemunits_option(): retrieve the current value of an option

Options for the chemunits package

  • preferred_units (character vector of units): the default units that new units (i.e. resulting from calculations) should be converted to. Default: "1" (i.e. units that cancel themselves and should be dimensionless are converted to unitless). The order does not matter except if units can be interconverted from each other (e.g. "L" and "m^3") in which case the first one will be used (with a warning).

  • auto_scale_units (character vector of units): the units whose best SI prefix (e.g. nano/n, micro/u, milli/m, kilo/k, etc) should be determined automatically based on the median value of a vector in this unit. Default: character(0) (i.e. no units are automatically scaled).

Examples

# Default setting(s):
old <- chemunits_options()
old # original options
#> $preferred_units
#> [1] "mol"   "g"     "g/mol" "M/bar" "M"     "L"     "1"    
#> 
#> $auto_scale_units
#> [1] "mol"   "g"     "g/mol" "M/bar" "M"     "L"    
#> 
get_chemunits_option("preferred_units")
#> [1] "mol"   "g"     "g/mol" "M/bar" "M"     "L"     "1"    

# with this, there is no default unit defined for energy or volume
# so the units are not simplified
set_cu(100, "W") * set_cu(1, "s")
#> 100 [W*s]
set_cu(1, "m") * set_cu(1, "mm^2")
#> 1 [mL]

# however the default does simplify dimensionless units
set_cu(1, "W*s") / set_cu(1, "J")
#> 1 [1]

# Change for the duration of the session:
chemunits_options(preferred_units = c("J", "L"))

# now W*s is recognized as energy and cm mm^2 as a volume and both are
# automatically converted to the specified default units
set_cu(100, "W") * set_cu(1, "s")
#> 100 [J]
set_cu(1, "m") * set_cu(1, "mm^2")
#> 1 [mL]

# however since "1" was no longer included in the `preferred_units`, 
# dimensionless units were no longer simplified (thus it is advisable
# to always include "1" in the `preferred_units` option)
set_cu(1, "W*s") / set_cu(1, "J")
#> 1 [W*s/J]

# Restore original values
chemunits_options(old)