"VSSem" <-
function (x,n=8,rotate="varimax",diagonal=FALSE,pc="pa",n.obs=NULL,...) #apply the Very Simple Structure Criterion for up to n factors on data set x
#find the maximum likelihood goodness of fit criterion
#x is a data matrix
#n is the maximum number of factors to extract (default is 8)
#rotate is a string "none" or "varimax" for type of rotation (default is "none"
#diagonal is a boolean value for whether or not we should count the diagonal (default=FALSE)
# ... other parameters for factanal may be passed as well
#e.g., to do VSS on a covariance/correlation matrix with up to 8 factors and 3000 cases:
#VSS(covmat=msqcovar,n=8,rotate="none",n.obs=3000)
{ #start Function definition
#first some preliminary functions
#complexrow sweeps out all except the c largest loadings
#complexmat applies complexrow to the loading matrix
complexrow <- function(x,c) #sweep out all except c loadings
{ n=length(x) #how many columns in this row?
temp <- x #make a temporary copy of the row
x <- rep(0,n) #zero out x
for (j in 1:c)
{
locmax <- which.max(abs(temp)) #where is the maximum (absolute) value
x[locmax] <- sign(temp[locmax])*max(abs(temp)) #store it in x
temp[locmax] <- 0 #remove this value from the temp copy
}
return(x) #return the simplified (of complexity c) row
}
complexmat <- function(x,c) #do it for every row (could tapply somehow?)
{
nrows <- dim(x)[1]
ncols <- dim(x)[2]
for (i in 1:nrows)
{x[i,] <- complexrow(x[i,],c)} #simplify each row of the loading matrix
return(x)
}
#now do the main Very Simple Structure routine
complexfit <- array(0,dim=c(n,n)) #store these separately for complex fits
complexchi <- array(0,dim=c(n,n))
complexchi2 <- array(0,dim=c(n,n))
complexdof <- array(0,dim=c(n,n))
complexresid <- array(0,dim=c(n,n))
vss.df <- data.frame(dof=rep(0,n),chisq=0,prob=0,sqresid=0,fit=0) #keep the basic results here
if (dim(x)[1]!=dim(x)[2]) { n.obs <- dim(x)[1]
x <- cor(x,use="pairwise") } else {if(!is.matrix(x)) x <- as.matrix(x)}
# if given a rectangular
if(is.null(n.obs)) {message("n.obs was not specified and was arbitrarily set to 1000. This only affects the chi square values.")
n.obs <- 1000}
if (n > dim(x)[2]) {n <- dim(x)[2]} #in cases where there are very few variables
n.variables <- dim(x)[2]
for (i in 1:n) #loop through 1 to the number of factors requested
{
if(!(pc=="pc")) { if ( pc=="pa") {
f <- fa(x,i,fm="pa",rotate=rotate,n.obs=n.obs,...) #do a factor analysis with i factors and the rotations specified in the VSS call
if (i==1)
{original <- x #just find this stuff once
sqoriginal <- original*original #squared correlations
totaloriginal <- sum(sqoriginal) - diagonal*sum(diag(sqoriginal) ) #sum of squared correlations - the diagonal
}} else {
f <- fa(x,i,fm=pc,rotate=rotate,covmat=x,n.obs=n.obs,...) #do a factor analysis with i factors and the rotations specified in the VSS call
if (i==1)
{original <- x #just find this stuff once
sqoriginal <- original*original #squared correlations
totaloriginal <- sum(sqoriginal) - diagonal*sum(diag(sqoriginal) ) #sum of squared correlations - the diagonal
}}
} else {f <- principal(x,i)
if (i==1)
{original <- x #the input to pc is a correlation matrix, so we don't need to find it again
sqoriginal <- original*original #squared correlations
totaloriginal <- sum(sqoriginal) - diagonal*sum(diag(sqoriginal) ) #sum of squared correlations - the diagonal
}
if((rotate=="varimax") & (i>1)) {f <- varimax(f$loadings)} else {
if((rotate=="promax") & (i>1)) {f <- promax(f$loadings)}
}}
load <- as.matrix(f$loadings ) #the loading matrix
model <- load %*% t(load) #reproduce the correlation matrix by the factor law R= FF'
residual <- original-model #find the residual R* = R - FF'
sqresid <- residual*residual #square the residuals
totalresid <- sum(sqresid)- diagonal * sum(diag(sqresid) ) #sum squared residuals - the main diagonal
fit <- 1-totalresid/totaloriginal #fit is 1-sumsquared residuals/sumsquared original (of off diagonal elements
if ((pc!="pc")) { #factor.pa reports the same statistics as mle, although the fits are not as good
vss.df[i,1] <- f$dof #degrees of freedom from the factor analysis
vss.df[i,2] <- f$STATISTIC #chi square from the factor analysis
vss.df[i,3] <- f$PVAL #probability value of this complete solution
}
vss.df[i,4] <- totalresid #residual given complete model
vss.df[i,5] <- fit #fit of complete model
#now do complexities -- how many factors account for each item
for (c in 1:i)
{
simpleload <- complexmat(load,c) #find the simple structure version of the loadings for complexity c
model <- simpleload%*%t(simpleload) #the model is now a simple structure version R ? SS'
residual <- original- model #R* = R - SS'
sqresid <- residual*residual
totalsimple <- sum(sqresid) -diagonal * sum(diag(sqresid)) #default is to not count the diagonal
simplefit <- 1-totalsimple/totaloriginal
complexresid[i,c] <-totalsimple
complexfit[i,c] <- simplefit
#find the chi square value for this level of complexity (see factor.pa for more details on code)
diag(model) <- 1
model.inv <- solve(model)
nfactors <- i
m.inv.r <- model.inv %*% original
dof <- n.variables * (n.variables-1)/2 - n.variables * c + (nfactors *(nfactors-1)/2)
objective <- sum(diag((m.inv.r))) - log(det(m.inv.r)) -n.variables
if (!is.null(n.obs)) {STATISTIC <- objective * (n.obs-1) -(2 * n.variables + 5)/6 -(2*nfactors)/3
if (dof > 0) {PVAL <- pchisq(STATISTIC, dof, lower.tail = FALSE)} else PVAL <- NA}
complexchi[i,c] <- STATISTIC
complexdof[i,c] <- dof
res1 <- residual
diag(res1) <- 1
complexchi2[i,c] <- -(n.obs - n.variables/3 -1.8) *log(det(res1))
}
} #end of i loop for number of factors
vss.stats <- data.frame(vss.df,cfit=complexfit,chisq=complexchi,complexchi2,complexdof,cresidual=complexresid)
return(vss.stats)
} #end of VSS function
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.