R: Additive logratio coordinates

addLR {robCompositions} | R Documentation

## 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))

### 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)`.

### 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 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.

### 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

`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)

[Package robCompositions version 2.1.0 Index]