##' space extension for training data
##' @export
extspace_dat <-
function(xdata)
{
#FIRST convert all catergorical values (factors) into binary values
#0+ to del Intercept produced by model.matrix
xdata=model.matrix(~0+.,as.data.frame(xdata))
# candidate variable for genereation
p=ncol(xdata)
d=p
ncomb <- combn(p, 2)
ncombsub <- ncomb[, sample(choose(p,2), d)]
newx<- vector(mode = "list", length = d)
newx<-NULL
new_names <- paste("newvar", 1:d, sep="_")
for (i in 1:p){
newx=cbind(newx,xdata[,ncombsub[2,i]]-xdata[,ncombsub[1,i]])
}
colnames(newx)<-new_names
#random choose d new features
# choosing according to some log-rank standard
newxdata=cbind(xdata,newx)
return (list(newxdata=newxdata,ncombsub=ncombsub))
}
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