grc  R Documentation 
Fits a Goodman's RC association model (GRC) to a matrix of counts, and more generally, rowcolumn interaction models (RCIMs). RCIMs allow for unconstrained quadratic ordination (UQO).
grc(y, Rank = 1, Index.corner = 2:(1 + Rank),
str0 = 1, summary.arg = FALSE, h.step = 1e04, ...)
rcim(y, family = poissonff, Rank = 0, M1 = NULL,
weights = NULL, which.linpred = 1,
Index.corner = ifelse(is.null(str0), 0, max(str0)) + 1:Rank,
rprefix = "Row.", cprefix = "Col.", iprefix = "X2.",
offset = 0, str0 = if (Rank) 1 else NULL,
summary.arg = FALSE, h.step = 0.0001,
rbaseline = 1, cbaseline = 1,
has.intercept = TRUE, M = NULL,
rindex = 2:nrow(y), cindex = 2:ncol(y), iindex = 2:nrow(y), ...)
y 
For 
family 
A VGAM family function.
By default, the first linear/additive predictor
is fitted
using main effects plus an optional rank 
Rank 
An integer from the set
{0,..., 
weights 
Prior weights. Fed into

which.linpred 
Single integer.
Specifies which linear predictor is modelled as the sum of an
intercept, row effect, column effect plus an optional interaction
term. It should be one value from the set 
Index.corner 
A vector of 
rprefix, cprefix, iprefix 
Character, for rows and columns and interactions respectively. For labelling the indicator variables. 
offset 
Numeric. Either a matrix of the right dimension, else a single numeric expanded into such a matrix. 
str0 
Ignored if 
summary.arg 
Logical. If 
h.step 
A small positive value that is passed into

... 
Arguments that are passed
into 
M1 
The number of linear predictors of the VGAM 
rbaseline, cbaseline 
Baseline reference levels for the rows and columns. Currently stored on the object but not used. 
has.intercept 
Logical. Include an intercept? 
M, cindex 
For 
rindex, iindex 

Goodman's RC association model fits a reducedrank approximation
to a table of counts.
A Poisson model is assumed.
The log of each cell mean is decomposed as an
intercept plus a row effect plus a column effect plus a reducedrank
component. The latter can be collectively written A %*% t(C)
,
the product of two ‘thin’ matrices.
Indeed, A
and C
have Rank
columns.
By default, the first column and row of the interaction matrix
A %*% t(C)
is chosen
to be structural zeros, because str0 = 1
.
This means the first row of A
are all zeros.
This function uses options()$contrasts
to set up the row and
column indicator variables.
In particular, Equation (4.5) of Yee and Hastie (2003) is used.
These are called Row.
and Col.
(by default) followed
by the row or column number.
The function rcim()
is more general than grc()
.
Its default is a nointeraction model of grc()
, i.e.,
rank0 and a Poisson distribution. This means that each
row and column has a dummy variable associated with it.
The first row and first column are baseline.
The power of rcim()
is that many VGAM family functions
can be assigned to its family
argument.
For example,
uninormal
fits something in between a 2way
ANOVA with and without interactions,
alaplace2
with Rank = 0
is something like
medpolish
.
Others include
zipoissonff
and
negbinomial
.
Hopefully one day all VGAM family functions will
work when assigned to the family
argument, although the
result may not have meaning.
Unconstrained quadratic ordination (UQO) can be performed
using rcim()
and grc()
.
This has been called unconstrained Gaussian ordination
in the literature, however the word Gaussian has two
meanings which is confusing; it is better to use
quadratic because the bellshape response surface is meant.
UQO is similar to CQO (cqo
) except there are
no environmental/explanatory variables.
Here, a GLM is fitted to each column (species)
that is a quadratic function of hypothetical latent variables
or gradients.
Thus each row of the response has an associated site score,
and each column of the response has an associated optimum
and tolerance matrix.
UQO can be performed here under the assumption that all species
have the same tolerance matrices.
See Yee and Hadi (2014) for details.
It is not recommended that presence/absence data be inputted
because the information content is so low for each sitespecies
cell.
The example below uses Poisson counts.
An object of class "grc"
, which currently is the same as
an "rrvglm"
object.
Currently,
a rank0 rcim()
object is of class rcim0class
,
else of class "rcim"
(this may change in the future).
The function rcim()
is experimental at this stage and
may have bugs.
Quite a lot of expertise is needed when fitting and in its
interpretion thereof. For example, the constraint
matrices applies the reducedrank regression to the first
(see which.linpred
)
linear predictor and the other linear predictors are interceptonly
and have a common value throughout the entire data set.
This means that, by default,
family =
zipoissonff
is
appropriate but not
family =
zipoisson
.
Else set family =
zipoisson
and
which.linpred = 2
.
To understand what is going on, do examine the constraint
matrices of the fitted object, and reconcile this with
Equations (4.3) to (4.5) of Yee and Hastie (2003).
The functions temporarily create a permanent data frame
called .grc.df
or .rcim.df
, which used
to be needed by summary.rrvglm()
. Then these
data frames are deleted before exiting the function.
If an error occurs then the data frames may be present
in the workspace.
These functions set up the indicator variables etc. before calling
rrvglm
or
vglm
.
The ...
is passed into rrvglm.control
or
vglm.control
,
This means, e.g., Rank = 1
is default for grc()
.
The data should be labelled with rownames
and
colnames
.
Setting trace = TRUE
is recommended to monitor
convergence.
Using criterion = "coefficients"
can result in slow convergence.
If summary = TRUE
then y
can be a
"grc"
object, in which case a summary can be returned.
That is, grc(y, summary = TRUE)
is
equivalent to summary(grc(y))
.
It is not possible to plot a
grc(y, summary = TRUE)
or
rcim(y, summary = TRUE)
object.
Thomas W. Yee, with assistance from Alfian F. Hadi.
Yee, T. W. and Hastie, T. J. (2003). Reducedrank vector generalized linear models. Statistical Modelling, 3, 15–41.
Yee, T. W. and Hadi, A. F. (2014). Rowcolumn interaction models, with an R implementation. Computational Statistics, 29, 1427–1445.
Goodman, L. A. (1981). Association models and canonical correlation in the analysis of crossclassifications having ordered categories. Journal of the American Statistical Association, 76, 320–334.
rrvglm
,
rrvglm.control
,
rrvglmclass
,
summary.grc
,
moffset
,
Rcim
,
Select
,
Qvar
,
plotrcim0
,
cqo
,
multinomial
,
alcoff
,
crashi
,
auuc
,
olym08
,
olym12
,
poissonff
,
medpolish
.
# Example 1: Undergraduate enrolments at Auckland University in 1990
fitted(grc1 < grc(auuc))
summary(grc1)
grc2 < grc(auuc, Rank = 2, Index.corner = c(2, 5))
fitted(grc2)
summary(grc2)
model3 < rcim(auuc, Rank = 1, fam = multinomial,
M = ncol(auuc)1, cindex = 2:(ncol(auuc)1), trace = TRUE)
fitted(model3)
summary(model3)
# Median polish but not 100 percent reliable. Maybe call alaplace2()...
## Not run:
rcim0 < rcim(auuc, fam = alaplace1(tau = 0.5), trace=FALSE, maxit = 500)
round(fitted(rcim0), digits = 0)
round(100 * (fitted(rcim0)  auuc) / auuc, digits = 0) # Discrepancy
depvar(rcim0)
round(coef(rcim0, matrix = TRUE), digits = 2)
Coef(rcim0, matrix = TRUE)
# constraints(rcim0)
names(constraints(rcim0))
# Compare with medpolish():
(med.a < medpolish(auuc))
fv < med.a$overall + outer(med.a$row, med.a$col, "+")
round(100 * (fitted(rcim0)  fv) / fv) # Hopefully should be all 0s
## End(Not run)
# Example 2: 2012 Summer Olympic Games in London
## Not run: top10 < head(olym12, 10)
grc1.oly12 < with(top10, grc(cbind(gold, silver, bronze)))
round(fitted(grc1.oly12))
round(resid(grc1.oly12, type = "response"), digits = 1) # Resp. resids
summary(grc1.oly12)
Coef(grc1.oly12)
## End(Not run)
# Example 3: UQO; see Yee and Hadi (2014)
## Not run:
n < 100; p < 5; S < 10
pdata < rcqo(n, p, S, es.opt = FALSE, eq.max = FALSE,
eq.tol = TRUE, sd.latvar = 0.75) # Poisson counts
true.nu < attr(pdata, "latvar") # The 'truth'; site scores
attr(pdata, "tolerances") # The 'truth'; tolerances
Y < Select(pdata, "y", sort = FALSE) # Y matrix (n x S); the "y" vars
uqo.rcim1 < rcim(Y, Rank = 1,
str0 = NULL, # Delta covers entire n x M matrix
iindex = 1:nrow(Y), # RRR covers the entire Y
has.intercept = FALSE) # Suppress the intercept
# Plot 1
par(mfrow = c(2, 2))
plot(attr(pdata, "optimums"), Coef(uqo.rcim1)@A,
col = "blue", type = "p", main = "(a) UQO optimums",
xlab = "True optimums", ylab = "Estimated (UQO) optimums")
mylm < lm(Coef(uqo.rcim1)@A ~ attr(pdata, "optimums"))
abline(coef = coef(mylm), col = "orange", lty = "dashed")
# Plot 2
fill.val < NULL # Choose this for the new parameterization
plot(attr(pdata, "latvar"), c(fill.val, concoef(uqo.rcim1)),
las = 1, col = "blue", type = "p", main = "(b) UQO site scores",
xlab = "True site scores", ylab = "Estimated (UQO) site scores" )
mylm < lm(c(fill.val, concoef(uqo.rcim1)) ~ attr(pdata, "latvar"))
abline(coef = coef(mylm), col = "orange", lty = "dashed")
# Plots 3 and 4
myform < attr(pdata, "formula")
p1ut < cqo(myform, family = poissonff,
eq.tol = FALSE, trace = FALSE, data = pdata)
c1ut < cqo(Select(pdata, "y", sort = FALSE) ~ scale(latvar(uqo.rcim1)),
family = poissonff, eq.tol = FALSE, trace = FALSE, data = pdata)
lvplot(p1ut, lcol = 1:S, y = TRUE, pcol = 1:S, pch = 1:S, pcex = 0.5,
main = "(c) CQO fitted to the original data",
xlab = "Estimated (CQO) site scores")
lvplot(c1ut, lcol = 1:S, y = TRUE, pcol = 1:S, pch = 1:S, pcex = 0.5,
main = "(d) CQO fitted to the scaled UQO site scores",
xlab = "Estimated (UQO) site scores")
## End(Not run)
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.