robCompositions (version 2.4.1)

addLR: Additive logratio coordinates

Description

The additive logratio coordinates map D-part compositional data from the simplex into a (D-1)-dimensional real space.

Usage

addLR(x, ivar = ncol(x), base = exp(1))

Value

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

x.alr

the resulting coordinates

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 useful when an inverse mapping is applied on the ‘same’ data set.

Arguments

x

D-part compositional data

ivar

Rationing part

base

a positive or complex number: the base with respect to which logarithms are computed. Defaults to exp(1).

Author

Matthias Templ

Details

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

References

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

See Also

addLRinv, pivotCoord

Examples

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

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