#Given an n x p matrix x, this function returns a n x 1 vector
#corresponding to unique preceeding rows of x.  It is used in
#constructing a Lack of Fit test for regression models.
rowmatch<-function(x) {
  x<-as.matrix(x)
  u<-unique(x)
  xchar<-apply(x,1,function(x){paste(x,collapse="")})
  uchar<-apply(u,1,function(x){paste(x,collapse="")})
  charmatch(xchar,uchar)
}

#This function performs a Lack of Fit test for a linear
#regression model.
#
#rm - model object corresponding to a linear regression model.
lof<-function(rm) {
  mf<-model.frame(rm)
  x<-mf[,2:ncol(mf)]
  m<-rowmatch(x)
  if(length(m)==max(m)) stop("need at least one replicate")
  newdata<-data.frame(mf,m=m)
  u=paste(as.character(rm$call$formula)[2],"~","factor(m)")
  fm<-lm(as.formula(u),data=newdata)
  anova(rm,fm)
}