procrustes {vegan} | R Documentation |
Function procrustes
rotates a configuration to maximum similarity
with another configuration. Function protest
tests the
non-randomness (`significance') between two configurations.
procrustes(X, Y, scale = TRUE, symmetric = FALSE) summary(object, ...) plot(x, kind=1, choices=c(1,2), xlab, ylab, main, ar.col = "blue", len=0.05, ...) residuals(object, ...) fitted(object, truemean = TRUE, ...) protest(X, Y, permutations = 1000, strata)
X |
Target matrix |
Y |
Matrix to be rotated. |
scale |
Allow scaling of axes of Y . |
symmetric |
Use symmetric Procrustes statistic (the rotation will still be non-symmetric). |
x, object |
An object of class procrustes . |
kind |
The kind of plot produced: kind=1 plots shifts in
two configurations and kind=2 plots an impulse diagram of
residuals. |
choices |
Axes (dimensions) plotted. |
xlab, ylab |
Axis labels, if defaults unacceptable. |
main |
Plot title, if default unacceptable. |
truemean |
Use the original range of target matrix instead of centring the fitted values. |
permutations |
Number of permutation to assess the significance of the symmetric Procrustes statistic. |
strata |
An integer vector or factor specifying the strata for permutation. If supplied, observations are permuted only within the specified strata. |
ar.col |
Arrow colour. |
len |
Width of the arrow head. |
... |
Other parameters passed to functions. |
Procrustes rotation rotates a matrix to maximum similarity with a
target matrix minimizing sum of squared differences. Procrustes
rotation is typically used in comparison of ordination results. It is
particularly useful in comparing alternative solutions in
multidimensional scaling. If scale=FALSE
, the function only
rotates matrix Y
. If scale=TRUE
, it scales linearly
configuration Y
for maximum similarity. Since Y
is scaled
to fit X
, the scaling is non-symmetric. However, with
symmetric=TRUE
, the configurations are scaled to equal
dispersions and a symmetric version of the Procrustes statistic
is computed.
Instead of matrix, X
and Y
can be results from an
ordination from which scores
can extract results.
Function plot
plots a procrustes
object and returns invisibly an ordiplot
object so that
function identify.ordiplot
can be used for identifying
points. The items in the ordiplot
object are called
heads
and points
with kind=1
(ordination diagram)
and sites
with kind=2
(residuals). In ordination
diagrams, the arrow heads point to the target configuration, which may
be either logical or illogical. Function plot
passes
parameters to underlying plotting functions.
Function residuals
returns the pointwise
residuals, and fitted
the fitted values, either centred to zero
mean (if truemean=FALSE
) or with the original scale (these
hardly make sense if symmetric = TRUE
). In
addition, there are summary
and print
methods.
If matrix X
has a lower number of columns than matrix
Y
, then matrix X
will be filled with zero columns to
match dimensions. This means that the function can be used to rotate
an ordination configuration to an environmental variable (most
practically extracting the result with the fitted
function).
Function protest
calls procrustes(..., symmetric = TRUE)
repeatedly to estimate the `significance' of the Procrustes
statistic. Function protest
uses a correlation-like statistic
derived from the symmetric Procrustes sum of squares ss as
r =sqrt{(1-ss)}, and sometimes called m_{12}. Function
protest
has own print
method, but otherwise uses
procrustes
methods. Thus plot
with a protest
object
yields a ``Procrustean superimposition plot.''
Function procrustes
returns an object of class
procrustes
with items. Function protest
inherits from
procrustes
, but amends that with some new items:
Yrot |
Rotated matrix Y . |
X |
Target matrix. |
ss |
Sum of squared differences between X and Yrot . |
rotation |
Orthogonal rotation matrix. |
translation |
Translation of the origin. |
scale |
Scaling factor. |
symmetric |
Type of ss statistic. |
call |
Function call. |
t0 |
This and the following items are only in class
protest : Procrustes correlation from non-permuted solution. |
t |
Procrustes correlations from permutations. |
signif |
`Significance' of t |
permutations |
Number of permutations. |
strata |
The name of the stratifying variable. |
stratum.values |
Values of the stratifying variable. |
The function protest
follows Peres-Neto & Jackson (2001),
but the implementation is still after Mardia et al.
(1979).
Jari Oksanen
Mardia, K.V., Kent, J.T. and Bibby, J.M. (1979). Multivariate Analysis. Academic Press.
Peres-Neto, P.R. and Jackson, D.A. (2001). How well do multivariate data sets match? The advantages of a Procrustean superimposition approach over the Mantel test. Oecologia 129: 169-178.
isoMDS
, initMDS
for obtaining
objects for procrustes
, and mantel
for an
alternative to protest
without need of dimension reduction.
data(varespec) vare.dist <- vegdist(wisconsin(varespec)) library(MASS) ## isoMDS library(mva) ## cmdscale to start isoMDS mds.null <- isoMDS(vare.dist, tol=1e-7) ## This was a good seed for me: your rng may vary. set.seed(237) mds.alt <- isoMDS(vare.dist, initMDS(vare.dist), maxit=200, tol=1e-7) vare.proc <- procrustes(mds.alt$points, mds.null$points) vare.proc summary(vare.proc) plot(vare.proc) plot(vare.proc, kind=2) residuals(vare.proc) ## Reset rng: rm(.Random.seed)