Different titles for plots using loop in R

Question

I am trying to make plots in a loop. But how do I put different titles on each plot? In this example, I want different names for my 8 density plots, such as beta[Treatment], beta[Time Dummy], etc. Thanks!

par(mfrow=c(4,2)
for (i in 2:8) {
  plot(density(beta[,i]))
  title(main=substitute(paste('Density of ', beta[Treatment]))))
}

Answer 1

tvec <- c("Treatment", "Time Dummy")

par(mfrow=c(2,1))
for(i in 1:2){
    plot(density(beta[,i]), 
         main=substitute(paste('Density of ', beta[a]), list(a=tvec[i])))
    }

Or actually if the name of your subscripts is the name of the columns of beta:

par(mfrow=c(4,2))
for(i in 2:8){
    plot(density(beta[,i]), 
         main=substitute(paste('Density of ', beta[a]), list(a=colnames(beta)[i])))
    }