Movatterモバイル変換

Version:	1.0-0
Title:	Measurement Units for R Vectors
Depends:	R (≥ 3.5.0)
Imports:	Rcpp
LinkingTo:	Rcpp (≥ 0.12.10)
Suggests:	NISTunits, measurements, xml2, magrittr, pillar (≥ 1.3.0),dplyr (≥ 1.0.0), vctrs (≥ 0.3.1), ggplot2 (> 3.2.1), testthat(≥ 3.0.0), vdiffr, knitr, rvest, rmarkdown
VignetteBuilder:	knitr
Description:	Support for measurement units in R vectors, matrices and arrays: automatic propagation, conversion, derivation and simplification of units; raising errors in case of unit incompatibility. Compatible with the POSIXct, Date and difftime classes. Uses the UNIDATA udunits library and unit database for unit compatibility checking and conversion. Documentation about 'units' is provided in the paper by Pebesma, Mailund & Hiebert (2016, <doi:10.32614/RJ-2016-061>), included in this package as a vignette; see 'citation("units")' for details.
SystemRequirements:	udunits-2
License:	GPL-2
URL:	https://r-quantities.github.io/units/,https://github.com/r-quantities/units
BugReports:	https://github.com/r-quantities/units/issues
RoxygenNote:	7.3.3
Encoding:	UTF-8
Config/testthat/edition:	3
NeedsCompilation:	yes
Packaged:	2025-10-05 19:45:48 UTC; edzer
Author:	Edzer Pebesma [aut, cre], Thomas Mailund [aut], Tomasz Kalinowski [aut], James Hiebert [ctb], Iñaki Ucar [aut], Thomas Lin Pedersen [ctb]
Maintainer:	Edzer Pebesma <edzer.pebesma@uni-muenster.de>
Repository:	CRAN
Date/Publication:	2025-10-09 10:40:02 UTC

Mathematical operations for units objects

Description

Mathematical operations for units objects

Usage

## S3 method for class 'units'Math(x, ...)

Arguments

Details

Logarithms receive a special treatment by the underlyingudunits2library. If a natural logarithm is applied to someunit, the result isln(re 1 unit), which meansnatural logarithm referenced to1 unit. For base 2 and base 10 logarithms, the outputlb(...)andlg(...) respectively instead ofln(...).

This is particularly important for some units that are typically expressed ina logarithmic scale (i.e.,bels, or, more commonly,decibels),such as Watts or Volts. For some of these units, the defaultudunits2database contains aliases: e.g.,BW (bel-Watts) is an alias oflg(re 1 W);Bm (bel-milliWatts) is an alias oflg(re 0.001 W);BV is an alias oflg(re 1 V) (bel-Volts),and so on and so forth (see the output ofvalid_udunits() for furtherreference).

Additionally, theunits package definesB, thebel, bydefault (because it is not defined byudunits2) as an alias oflg(re 1), unless a user-provided XML database already contains adefinition ofB, or thedefine_bel option is set toFALSE(seehelp(units_options)).

Examples

# roundings, cummulative functionsx <- set_units(sqrt(1:10), m/s)signif(x, 2)cumsum(x)# trigonometrysin(x) # not meaningfulx <- set_units(sqrt(1:10), rad)sin(x)cos(x)x <- set_units(seq(0, 1, 0.1), 1)asin(x)acos(x)# logarithmsx <- set_units(sqrt(1:10), W)log(x) # base exp(1)log(x, base = 3)log2(x)log10(x)set_units(x, dBW) # decibel-wattsset_units(x, dBm) # decibel-milliwatts

S3 Ops Group Generic Functions for units objects

Description

Ops functions for units objects, including comparison, product and divide,add, subtract.

Usage

## S3 method for class 'units'Ops(e1, e2)

Arguments

Details

Users are advised against performing arithmetical operations withtemperatures in different units. Theunits package ensure that results1) are arithmetically correct, and 2) satisfy dimensional analysis, but couldnever ensure that results are physically meaningful. Temperature units arespecial because there is an absolute unit, Kelvin, and relative ones, Celsiusand Fahrenheit degrees. Arithmetic operations between them are meaninglessfrom the physical standpoint. Users are thus advised to convert alltemperatures to Kelvin before operating.

Value

object of classunits

Examples

a <- set_units(1:3, m/s)b <- set_units(1:3, m/s)a + ba * ba / ba <- as_units("kg m-3")b <- set_units(1, kg/m/m/m)a + ba = set_units(1:5, m)a %/% aa %/% set_units(2)set_units(1:5, m^2) %/% set_units(2, m)a %% aa %% set_units(2)

convert units object into difftime object

Description

convert units object into difftime object

Usage

as_difftime(x)

Arguments

Examples

t1 = Sys.time()t2 = t1 + 3600d = t2 - t1du <- as_units(d)dt = as_difftime(du)class(dt)dt

boxplot for unit objects

Description

boxplot for unit objects

Usage

## S3 method for class 'units'boxplot(x, ..., horizontal = FALSE)

Arguments

Examples

units_options(parse = FALSE) # otherwise we break on the funny symbol!u = set_units(rnorm(100), degree_C)boxplot(u)

Combine R Objects by Rows or Columns

Description

S3 methods forunits objects (seecbind).

Usage

## S3 method for class 'units'cbind(..., deparse.level = 1)## S3 method for class 'units'rbind(..., deparse.level = 1)

Arguments

Examples

x <- set_units(1, m/s)y <- set_units(1:3, m/s)z <- set_units(8:10, m/s)(m <- cbind(x, y)) # the '1' (= shorter vector) is recycled(m <- cbind(m, z)[, c(1, 3, 2)]) # insert a column(m <- rbind(m, z)) # insert a row

Convert units to their base units

Description

Convert the units of aunits object to their base units, as defined bythe udunits database (SI units).

Usage

convert_to_base(x, simplify = TRUE, keep_fraction = TRUE)

Arguments

Value

object of classunits with units converted to base units.

Examples

x <- set_units(32, mJ/g)convert_to_base(x)convert_to_base(x, keep_fraction=FALSE)convert_to_base(x, simplify=FALSE)convert_to_base(x, simplify=FALSE, keep_fraction=FALSE)

deparse unit to string in product power form (e.g. km m-2 s-1)

Description

deparse unit to string in product power form (e.g. km m-2 s-1)

Usage

deparse_unit(x)

Arguments

Value

length one character vector

Examples

u = as_units("kg m-2 s-1")udeparse_unit(u)

Drop Units

Description

Drop units attribute and class.

Usage

drop_units(x)## S3 method for class 'units'drop_units(x)## S3 method for class 'data.frame'drop_units(x)## S3 method for class 'mixed_units'drop_units(x)

Arguments

Details

Equivalent tounits(x) <- NULL, or the pipe-friendly versionset_units(x, NULL), butdrop_units will fail if the object hasno units metadata. Use the alternatives if you want this operation to succeedregardless of the object type.

Adata.frame method is also provided, which checks every column anddrops units if any.

Value

the numeric without any units attributes, while preserving otherattributes like dimensions or other classes.

Examples

x <- 1y <- set_units(x, m/s)# this succeedsdrop_units(y)set_units(y, NULL)set_units(x, NULL)## Not run: # this failsdrop_units(x)## End(Not run)df <- data.frame(x=x, y=y)dfdrop_units(df)

histogram for unit objects

Description

histogram for unit objects

Usage

## S3 method for class 'units'hist(x, xlab = NULL, main = paste("Histogram of", xname),  ...)

Arguments

Examples

units_options(parse = FALSE) # otherwise we break on the funny symbol!u = set_units(rnorm(100), degree_C)hist(u)

Define or remove units

Description

Installing new symbols and/or names allows them to be used inas_units,make_units andset_units. Optionally, a relationship can bedefined 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

Details

At least one symbol or name is expected, but multiple symbols and/or namescan be installed (and thus mapped to the same unit) or removed at the sametime. Thedef argument enables arbitrary relationships with existingunits using UDUNITS-2 syntax:

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 seeexamples of string unit specifications.

Examples

# define a fortnightinstall_unit("fn", "2 week", "fortnight")year <- as_units("year")set_units(year, fn)        # by symbolset_units(year, fortnight) # by name# clean upremove_unit("fn", "fortnight")# working with currenciesinstall_unit("dollar")install_unit("euro", "1.22 dollar")install_unit("yen", "0.0079 euro")set_units(as_units("dollar"), yen)# clean upremove_unit(c("dollar", "euro", "yen"))# an example from microbiologycfu_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 upremove_unit(c("cell", cfu_symbols), cfu_names)

Apply a function keeping units

Description

Helper function to apply a function to aunits object and then restorethe original units.

Usage

keep_units(FUN, x, ..., unit = units(x))

Arguments

Details

Provided for incompatible functions that do not preserve units. The user isresponsible for ensuring the correctness of the output.

Ifx is not aunits objectandunit is not provided by the user,a warning is issued, and the output will also have no units(see examples).

Value

An object of classunits.

Examples

x <- set_units(1:5, m)keep_units(drop_units, x)# An example use case is with random number generating functions:mu <- as_units(10, "years")keep_units(rnorm, n = 1, x = mu)# units can be directly specified if needed; for example, with# `rexp()`, the units of the rate parameter are the inverse of# the units of the output:rate <- as_units(3, "1/year")keep_units(rexp, n = 1, x = rate, unit = units(1/rate))# if `x` does not actually have units, a warning is issued,# and the output has no units:rate2 <- 3keep_units(rexp, n = 1, x = rate2)

Load a unit system

Description

Load an XML database containing a unit system compatible with UDUNITS2.

Usage

load_units_xml(path = default_units_xml())

Arguments

Details

A unit system comprises a root<unit-system> and a number of childrendefining prefixes (<prefix>) or units (<unit>).See the contents of

system.file("share/udunits", package="units")

for examples.

Examples

# load a new unit systemload_units_xml(system.file("share/udunits/udunits2-base.xml", package="units"))## Not run: set_units(1, rad) # doesn'twork## End(Not run)# reload the default unit systemload_units_xml()set_units(1, rad) # works again

S3 matrixOps Group Generic Functions for units objects

Description

matrixOps functions for units objects.

Usage

## S3 method for class 'units'matrixOps(x, y)

Arguments

Value

object of classunits

Examples

a = set_units(1:5, m)a %*% aa %*% t(a)a %*% 1:51:5 %*% a

Create or convert to a mixed units list-column

Description

Create or convert to a mixed units list-column

Usage

mixed_units(x, values, ...)## S3 replacement method for class 'mixed_units'units(x) <- value

Arguments

Details

ifx is of classunits,values should be missing or of classmixed_symbolic_units; ifx is numeric,values should be a character vector the length ofx.

Examples

a <- 1:4u <- c("m/s", "km/h", "mg/L", "g")mixed_units(a, u)units(a) = as_units("m/s")mixed_units(a) # converts to mixed representation

Plotunits objects

Description

Create axis label with appropriate labels.

Plot method forunits objects.

Usage

make_unit_label(lab, u, sep = units_options("sep"),  group = units_options("group"), parse = units_options("parse"))## S3 method for class 'units'plot(x, y, xlab = NULL, ylab = NULL, ...)

Arguments

Details

units_options can be used to set and change the defaults forsep,group anddoParse.

Examples

displacement = mtcars$disp * as_units("in")^3units(displacement) = make_units(cm^3)weight = mtcars$wt * 1000 * make_units(lb)units(weight) = make_units(kg)plot(weight, displacement)units_options(group = c("(", ")") )  # parenthesis instead of square bracketsplot(weight, displacement)units_options(sep = c("~~~", "~"), group = c("", ""))  # no brackets; extra spaceplot(weight, displacement)units_options(sep = c("~", "~~"), group = c("[", "]"))gallon = as_units("gallon")consumption = mtcars$mpg * make_units(mi/gallon)units(consumption) = make_units(km/l)plot(displacement, consumption) # division in consumptionunits_options(negative_power = TRUE) # division becomes ^-1plot(displacement, consumption)plot(1/displacement, 1/consumption)

Continuous scales for units data

Description

These are the default scales for theunits class. These will usuallybe added automatically. To override manually, usescale_{type}_units.

Usage

scale_x_units(..., sec.axis = ggplot2::waiver(), unit = NULL)scale_y_units(..., sec.axis = ggplot2::waiver(), unit = NULL)scale_colour_units(..., unit = NULL)scale_color_units(..., unit = NULL)scale_fill_units(..., unit = NULL)scale_alpha_units(..., unit = NULL)scale_size_units(..., unit = NULL)scale_size_area_units(..., unit = NULL)scale_radius_units(..., unit = NULL)scale_linewidth_units(..., unit = NULL)

Arguments

Examples

if (requireNamespace("ggplot2", quietly=TRUE)) {library(ggplot2)mtcars$consumption <- set_units(mtcars$mpg, mi / gallon)mtcars$power <- set_units(mtcars$hp, hp)# Use units encoded into the dataggplot(mtcars) +  geom_point(aes(power, consumption))# Convert units on the fly during plottingggplot(mtcars) +  geom_point(aes(power, consumption)) +  scale_x_units(unit = "W") +  scale_y_units(unit = "km/l")# Resolve units when transforming dataggplot(mtcars) +  geom_point(aes(power, 1 / consumption))# Reverse the y axisggplot(mtcars) +  geom_point(aes(power, consumption)) +  scale_y_units(transform="reverse")}

seq method for units objects

Description

seq method for units objects

Usage

## S3 method for class 'units'seq(from, to, by = ((to - from)/(length.out - 1)),  length.out = NULL, along.with = NULL, ...)

Arguments

Details

arguments with units are converted to have units of the first argument (which is eitherfrom orto)

Examples

seq(to = set_units(10, m), by = set_units(1, m), length.out = 5)seq(set_units(10, m), by = set_units(1, m), length.out = 5)seq(set_units(10, m), set_units(19, m))seq(set_units(10, m), set_units(.1, km), set_units(10000, mm))

udunits2 utilities

Description

Someudunits2 utilities are exposed to the user. These functions areuseful for checking whether units are convertible or converting between unitswithout having to createunits objects.Arguments are recycled if necessary.

Usage

ud_are_convertible(from, to, ...)ud_convert(x, from, to)

Arguments

Value

ud_are_convertiblereturnsTRUE if both units exist and are convertible,FALSE otherwise.

ud_convertreturns a numeric vector withx converted to new unit.

Examples

ud_are_convertible(c("m", "mm"), "km")ud_convert(c(100, 100000), c("m", "mm"), "km")a <- set_units(1:3, m/s)ud_are_convertible(units(a), "km/h")ud_convert(1:3, units(a), "km/h")ud_are_convertible("degF", "degC")ud_convert(32, "degF", "degC")

The "unit" type for vectors that are actually dimension-less.

Description

The "unit" type for vectors that are actually dimension-less.

Usage

unitless

Format

An object of classsymbolic_units of length 2.

Handle measurement units

Description

A number of functions are provided for handling unit objects.

• `units<-` andunits are the basic functions to setand retrieve units.

• as_units, a generic with methods for acharacter string and for quoted language. Note, direct usage of this functionby users is typically not necessary, as coercion viaas_units isautomatically done with`units<-` andset_units.

• make_units, constructs units from bare expressions.make_units(m/s) is equivalent toas_units(quote(m/s)).

• set_units, a pipe-friendly version of`units<-`. Bydefault it operates with bare expressions, but thisbehavior can be disabled by a specifyingmode = "standard" or settingunits_options(set_units_mode = "standard").Ifvalue is missing or set to1, the object becomes unitless.

Usage

## S3 replacement method for class 'numeric'units(x) <- value## S3 replacement method for class 'units'units(x) <- value## S3 replacement method for class 'logical'units(x) <- value## S3 method for class 'units'units(x)## S3 method for class 'symbolic_units'units(x)set_units(x, value, ..., mode = units_options("set_units_mode"))make_units(bare_expression, check_is_valid = TRUE)as_units(x, ...)## Default S3 method:as_units(x, value = unitless, ...)## S3 method for class 'units'as_units(x, value, ...)## S3 method for class 'symbolic_units'as_units(x, value, ...)## S3 method for class 'difftime'as_units(x, value, ...)## S3 method for class 'character'as_units(x, ..., check_is_valid = TRUE,  force_single_symbol = FALSE)## S3 method for class 'call'as_units(x, ...)## S3 method for class 'expression'as_units(x, ...)## S3 method for class 'name'as_units(x, ...)## S3 method for class 'POSIXt'as_units(x, value, ...)## S3 method for class 'Date'as_units(x, value, ...)

Arguments

Details

Ifvalue is of classunits and has a value unequal to 1, thisvalue is ignored unlessunits_options("simplifiy") isTRUE. Ifsimplify isTRUE,x is multiplied by this value.

Value

An object of classunits.

Theunits method retrieves the units attribute, which is ofclasssymbolic_units.

Character strings

Generally speaking, there are 3 types of unit strings are accepted inas_units (and by extension,`units<-`).

The first type, and likely most common, is a "standard" format unitspecification where the relationship between unit symbols or names isspecified explicitly with arithmetic symbols for division/,multiplication* and power exponents^.

The second type of unit string accepted is one with implicit exponents. Inthis format,/,*, and^, may not be present in thestring, and unit symbol or names must be separated by a space. Each unitsymbol may optionally be followed by a single number, specifying the power.For example"m2 s-2" is equivalent to"(m^2)*(s^-2)".

If the string supplied fails to parse, then the string is treated as asingle symbolic unit andsymbolic_unit(chr) is used as a fallbackwith a warning. In that case, automatic unit simplification may not workproperly when performing operations on unit objects, but unit conversionand other Math operations should still give correct results so long asthe unit string supplied returnsTRUE forud_is_parsable().

It must be noted that prepended numbers are supported too, but are nottreated as magnitudes. For example,"1000 m" is interpreted asa prefixed unit, and it is equivalent to"km" to all effects.

The third type of unit string format accepted is the special case ofudunits time duration with a reference origin, for example"hours since 1970-01-01 00:00:00". Note, that the handling of time and calendaroperations via the udunits library is subtly different from the way Rhandles date and time operations. This functionality is mostly exported forusers that work with udunits time data, e.g., with NetCDF files. Users areotherwise encouraged to useR's date and time functionality providedbyDate andPOSIXt classes.

Note

By default, unit names are automatically substituted with unit names(e.g., kilogram –> kg). To turn off this behavior, setunits_options(auto_convert_names_to_symbols = FALSE)

See Also

install_unit,valid_udunits

Examples

x = 1:3class(x)units(x) <- as_units("m/s")class(x)y = 2:5a <- set_units(1:3, m/s)units(a) <- make_units(km/h)a# convert to a mixed_units object:units(a) <- c("m/s", "km/h", "km/h")a# The easiest way to assign units to a numeric vector is like this:x <- y <- 1:4units(x) <- "m/s"  # meters / second# Alternatively, the easiest pipe-friendly way to set units:if(requireNamespace("magrittr", quietly = TRUE)) {  library(magrittr)  y %>% set_units(m/s)}# these are different ways of creating the same unit:# meters per second squared, i.e, accelerationx1 <- make_units(m/s^2)x2 <- as_units(quote(m/s^2))x2 <- as_units("m/s^2")x3 <- as_units("m s-2") # in product power form, i.e., implicit exponents = Tx4 <- set_units(1,  m/s^2) # by default, mode = "symbols"x5 <- set_units(1, "m/s^2",   mode = "standard")x6 <- set_units(1, x1,        mode = "standard")x7 <- set_units(1, units(x1), mode = "standard")x8 <- as_units("m") / as_units("s")^2all_identical <- function(...) {  l <- list(...)  for(i in seq_along(l)[-1])    if(!identical(l[[1]], l[[i]]))      return(FALSE)  TRUE}all_identical(x1, x2, x3, x4, x5, x6, x7, x8)# Note, direct usage of these unit creation functions is typically not# necessary, since coercion is automatically done via as_units(). Again,# these are all equivalent ways to generate the same result.x1 <- x2 <- x3 <- x4 <- x5 <- x6 <- x7 <- x8 <- 1:4units(x1) <- "m/s^2"units(x2) <- "m s-2"units(x3) <- quote(m/s^2)units(x4) <- make_units(m/s^2)units(x5) <- as_units(quote(m/s^2))x6 <- set_units(x6, m/s^2)x7 <- set_units(x7, "m/s^2", mode = "standard")x8 <- set_units(x8, units(x1), mode = "standard")all_identical(x1, x2, x3, x4, x5, x6, x7, x8)# Both unit names or symbols can be used. By default, unit names are# automatically converted to unit symbols.make_units(degree_C)make_units(kilogram)make_units(ohm)## Arithmetic operations and units# conversion between unit objects that were defined as symbols and names will# work correctly, although unit simplification in printing may not always occur.x <- 500 * make_units(micrograms/liter)y <- set_units(200, ug/l)x + yx * y # numeric result is correct, but units not simplified completely# note, plural form of unit name accepted too ('liters' vs 'liter'), and# denominator simplification can be performed correctlyx * set_units(5, liters)# unit conversion works tooset_units(x, grams/gallon)## Creating custom, user defined units# For example, a microbiologist might work with counts of bacterial cells# make_units(cells/ml) # by default, throws an ERROR# First define the unit, then the newly defined unit is accepted.install_unit("cells")make_units(cells/ml)# Note that install_unit() adds support for defining relationships between# the newly created symbols or names and existing units.## set_units()# set_units is a pipe friendly version of `units<-`.if(requireNamespace("magrittr", quietly = TRUE)) {  library(magrittr)  1:5 %>% set_units(N/m^2)  # first sets to m, then converts to km  1:5 %>% set_units(m) %>% set_units(km)}# set_units has two modes of operation. By default, it operates with# bare symbols to define the units.set_units(1:5, m/s)# use `mode = "standard"` to use the value of supplied argument, rather than# the bare symbols of the expression. In this mode, set_units() can be# thought of as a simple alias for `units<-` that is pipe friendly.set_units(1:5, "m/s", mode = "standard")set_units(1:5, make_units(m/s), mode = "standard")# the mode of set_units() can be controlled via a global option# units_options(set_units_mode = "standard")# To remove units useunits(x) <- NULL# orset_units(x, NULL)# ordrop_units(y)s = Sys.time()d  = s - (s+1)as_units(d)

Defunct functions inunits

Description

These functions are no longer available.

Details

• ud_units: Useas_units instead.

• as.units: Useas_units instead.

• make_unit: Useas_units instead.

• parse_unit: Useas_units instead.

• as_cf: Usedeparse_unit instead.

• install_symbolic_unit: Useinstall_unit instead.

• remove_symbolic_unit: Useremove_unit instead.

• install_conversion_constant: Useinstall_unit instead.

• install_conversion_offset: Useinstall_unit instead.

set one or more units global options

Description

set units global options, mostly related how units are printed and plotted

Usage

units_options(..., sep, group, negative_power, parse, set_units_mode,  strict_tokenizer, auto_convert_names_to_symbols, simplify, allow_mixed,  unitless_symbol, define_bel)

Arguments

Details

This sets or gets units options. Set them by using named arguments, get them by passing the option name.

The defaultNA value forsimplify means units are not simplified inset_units oras_units, but are simplified in arithmetical expressions.

Value

in case options are set, invisibly a named list with the option values that are being set; if an option is queried, the current option value.

Examples

old = units_options(sep = c("~~~", "~"), group = c("", "")) # more space, parenthesisold## set back to defaults:units_options(sep = c("~", "~"), group = c("[", "]"), negative_power = FALSE, parse = TRUE)units_options("group")

Get information about valid units

Description

These functions require thexml2 package, and return data frames withcomplete information about pre-defined units from UDUNITS2. Inspect this dataframes to determine what inputs are accepted byas_units (and theother functions it powers:as_units,set_units ,units<-).

Usage

valid_udunits(quiet = FALSE)valid_udunits_prefixes(quiet = FALSE)

Arguments

Details

Any entry listed undersymbol ,symbol_aliases ,name_singular ,name_singular_aliases ,name_plural , orname_plural_aliases is valid. Additionally, any entry undersymbol orsymbol_aliases may can also contain a valid prefix,as specified byvalid_udunits_prefixes() .

Note, this is primarily intended for interactive use, the exact format of thereturned data frames may change in the future.

Value

a data frame with columnssymbol ,symbol_aliases ,name_singular ,name_singular_aliases ,name_plural ,orname_plural_aliases ,def ,definition ,comment ,dimensionless andsource_xml

Examples

if (requireNamespace("xml2", quietly = TRUE)) {  valid_udunits()  valid_udunits_prefixes()  if(interactive())    View(valid_udunits())}