# [R] help with formula for clogit

1Rnwb sbpurohit at gmail.com
Mon Nov 7 16:19:51 CET 2011

```I would like to know if clogit function can be used as below
clogit(group~., data=dataframe)

When I try to use in above format it takes a long time, I would appreciate
some pointers to get multiple combinations tested.

set.seed(100)
d=data.frame(x=rnorm(20)+5,
x1=rnorm(20)+5,
x2=rnorm(20)+5,
x3=rnorm(20)+5,
x4=rnorm(20)+5,
x5=rnorm(20)+5,
x6=rnorm(20)+5,
x7=rnorm(20)+5,
x8=rnorm(20)+5,
group=rep(c(1,2),10), Age=rnorm(20)+35,strata=c(rep(1,10), rep(2,10)))

nam=names(d)[1:9]
results <- c("Protein", "OR", "p-val")
pc3=combinations(n=length(nam),r=2)

for (len in 1:dim(pc3))
{
prs=pc3[len,]
mols=nam[prs]
d2=d[,c(mols,'group','Age','strata')]
log.reg<-clogit(group~.,data=d2)
a = summary(log.reg)\$conf.int
z= summary(log.reg)\$coefficients[1,4]  #ncol in coefficients is 3 * number
of parameters
pval  = 2*pnorm(-abs(z))
res2 = c(paste('IL8+',molecule,sep=''), paste (round(a[1,1],2), " ("  ,
round(a[1,3],2), " - " , round(a[1,4],2), ")" , sep=""), pval)
results  = rbind (results ,res2 )
}

Thanks