alr {robCompositions}R Documentation

Additive log-ratio transformation

Description

The alr transformation moves D-part compositional data from the simplex into a (D-1)-dimensional real space.

Usage

alr(x, ivar=ncol(x))

Arguments

x D-part compositional data
ivar Rationing part

Details

The compositional parts are divided by the rationing part before the logarithm is taken.

Value

A list of class “alr” which includes the following content:

x.alr the transformed data
varx the rationing variable
ivar the index of the rationing variable, indicating the column number of the rationing variable in the data matrix x
cnames the column names of x

The additional information such as cnames or ivar is usefull when a back-transformation is applied on the ‘same’ data set.

Author(s)

Matthias Templ

References

Aitchison, J. (1986) The Statistical Analysis of Compositional Data Monographs on Statistics and Applied Probability. Chapman & Hall Ltd., London (UK). 416p.

See Also

invalr, ilr, alr

Examples

data(arcticLake)
x <- arcticLake
x.alr <- alr(x, 2)
y <- invalr(x.alr)
## This exactly fulfills:
invalr(alr(x, 3))
data(expenditures)
x <- expenditures
y <- invalr(alr(x, 5))
head(x)
head(y)
## --> absolute values are preserved as well.

## preserve only the ratios:
invalr(x.alr, ivar=2, useClassInfo=FALSE)




[Package robCompositions version 1.3.3 Index]