units (version 0.8-5)

install_unit: Define or remove units

Description

Installing new symbols and/or names allows them to be used in as_units, make_units and set_units. Optionally, a relationship can be defined between such symbols/names and existing ones (see details and examples).

Usage

install_unit(symbol = character(0), def = character(0),
  name = character(0))
remove_unit(symbol = character(0), name = character(0))

Arguments

symbol

a vector of symbols to be installed/removed.

def

either

• an empty definition, which defines a new base unit;

• "unitless", which defines a new dimensionless unit;

• a relationship with existing units (see details for the syntax).

name

a vector of names to be installed/removed.

Details

At least one symbol or name is expected, but multiple symbols and/or names can be installed (and thus mapped to the same unit) or removed at the same time. The def argument enables arbitrary relationships with existing units using UDUNITS-2 syntax:

String Type	Using Names	Using Symbols	Comment
Simple	meter	m
Raised	meter^2	m2	higher precedence than multiplying or dividing
Product	newton meter	N.m
Quotient	meter per second	m/s
Scaled	60 second	60 s
Prefixed	kilometer	km
Offset	kelvin from 273.15	K @ 273.15	lower precedence than multiplying or dividing
Logarithmic	lg(re milliwatt)	lg(re mW)	"lg" is base 10, "ln" is base e, and "lb" is base 2
Grouped	(5 meter)/(30 second)	(5 m)/(30 s)

The above may be combined, e.g., "0.1 lg(re m/(5 s)^2) @ 50". You may also look at the <def> elements in the units database to see examples of string unit specifications.

Examples

# define a fortnight
install_unit("fn", "2 week", "fortnight")
year <- as_units("year")
set_units(year, fn)        # by symbol
set_units(year, fortnight) # by name
# clean up
remove_unit("fn", "fortnight")

# working with currencies
install_unit("dollar")
install_unit("euro", "1.22 dollar")
install_unit("yen", "0.0079 euro")
set_units(as_units("dollar"), yen)
# clean up
remove_unit(c("dollar", "euro", "yen"))

# an example from microbiology
cfu_symbols <- c("CFU", "cfu")
cfu_names <- c("colony_forming_unit", "ColonyFormingUnit")
install_unit("cell")
install_unit(cfu_symbols, "3.4 cell", cfu_names)
cell <- set_units(2.5e5, cell)
vol <- set_units(500, ul)
set_units(cell/vol, "cfu/ml")
set_units(cell/vol, "CFU/ml")
set_units(cell/vol, "colony_forming_unit/ml")
set_units(cell/vol, "ColonyFormingUnit/ml")
# clean up
remove_unit(c("cell", cfu_symbols), cfu_names)