idt {compositions} | R Documentation |
Compute the isometric default transform of a vector (or dataset) of compositions or amounts in the selected class.
idt(x,...) ## Default S3 method: idt( x,... ) ## S3 method for class 'acomp': idt( x ,...) ## S3 method for class 'rcomp': idt( x ,...) ## S3 method for class 'aplus': idt( x ,...) ## S3 method for class 'rplus': idt( x ,...) ## S3 method for class 'rmult': idt( x ,...) ## S3 method for class 'factor': idt( x ,...) idtInv(x,orig,...) ## Default S3 method: idtInv( x ,orig,...) ## S3 method for class 'acomp': idtInv( x ,orig,...) ## S3 method for class 'rcomp': idtInv( x ,orig,...) ## S3 method for class 'aplus': idtInv( x ,orig,...) ## S3 method for class 'rplus': idtInv( x ,orig,...) ## S3 method for class 'rmult': idtInv( x ,orig,...)
x |
a classed amount or composition, to be transformed with its isometric default transform, or its inverse |
... |
generic arguments past to underlying functions |
orig |
a compositional object which should be mimicked by the inverse transformation. It is used to determine the backtransform to be used, and eventually to reconstruct the names of the parts. It is the generic argument. Typically the orig-argument is the dataset that has been transformed in the first place. |
The general idea of this package is to analyse the same data with
different geometric concepts, in a fashion as similar as possible. For each of the
four concepts there exists an isometric transform expressing the geometry
in a full-rank euclidean vector space. Such a transformation is computed
by idt
. For acomp
the transform is ilr
, for
rcomp
it is ipt
, for
aplus
it is ilt
, and for
rplus
it is iit
. Keep in mind that the
transform does not keep the variable names, since there is no guaranteed
one-to-one relation between the original parts and each transformed
variable.
The inverse idtInv
is intended to allow for an "easy" and automatic
back-transformation, without intervention of the user. The argument orig
(the one determining the behaviour of idtInv
as a generic function)
tells the function which back-transformation should be applied, and
gives the column names of orig
to the back-transformed
values of x
. Therefore, it is very conventient to give the original classed
data set used in the analysis as orig
.
A corresponding matrix of row-vectors containing the transforms.
R. Tolosana-Delgado, K.Gerald v.d. Boogaart http://www.stat.boogaart.de
van den Boogaart, K.G. and R. Tolosana-Delgado (2008) "compositions": a unified R package to analyze Compositional Data, Computers & Geosciences, 34 (4), pages 320-338, doi:10.1016/j.cageo.2006.11.017.
cdt
, ilr
, ipt
,
ilt
, cdtInv
, ilrInv
, iptInv
,
iltInv
, iitInv
## Not run: # the idt is defined by idt <- function(x) UseMethod("idt",x) idt.default <- function(x) x idt.acomp <- function(x) ilr(x) idt.rcomp <- function(x) ipt(x) idt.aplus <- ilt idt.rplus <- iit ## End(Not run) idt(acomp(1:5)) idt(rcomp(1:5)) data(Hydrochem) x = Hydrochem[,c("Na","K","Mg","Ca")] y = acomp(x) z = idt(y) y2 = idtInv(z,y) par(mfrow=c(2,2)) for(i in 1:4){plot(y[,i],y2[,i])}