robCompositions (version 1.9.1)

addLR: Additive log-ratio transformation

Description

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

Usage

addLR(x, ivar=ncol(x))

Arguments

x

D-part compositional data

ivar

Rationing part

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.

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 & Hall Ltd., London (UK). 416p.

See Also

addLRinv, isomLR

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)