Additive logratio coordinates
The additive logratio coordinates map D-part compositional data from the simplex into a (D-1)-dimensional real space.
addLR(x, ivar = ncol(x), base = exp(1))
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 |
The compositional parts are divided by the rationing part before the logarithm is taken.
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.
Matthias Templ
Aitchison, J. (1986) The Statistical Analysis of Compositional Data Monographs on Statistics and Applied Probability. Chapman \& Hall Ltd., London (UK). 416p.
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)
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