How do I loop through a string in R?

Loop over string variables in R

• When programming in Stata I often find myself using the loop index in the programming. For example, I'll loop over a list of the variables nominalprice and realprice: local list = "nominalprice realprice" foreach i of local list { summarize `i' twoway (scatter `i' time) graph export "C:\TimePlot-`i'.png" } This will plot the time series of nominal and real prices and export one graph called TimePlot-nominalprice.png and another called TimePlot-realprice.png. In R the method I've come up with to do the same thing would be: clist <- c("nominalprice", "realprice") for (i in clist) { e <- paste("png(\"c:/TimePlot-",i,".png\")", sep="") eval(parse(text=e)) plot(time, eval(parse(text=i))) dev.off() } This R code looks unintuitive and messy to me and I haven't found a good way to do this sort of thing in R yet. Maybe I'm just not thinking about the problem the right way? Can you suggest a better way to loop using strings?

• Answer:

  As other people have intimated, this would be easier if you had a dataframe with columns named nominalprice and realprice. If you do not, you could always use get. You shouldn't need parse at all here. clist <- c("nominalprice", "realprice") for (i in clist) { png(paste("c:/TimePlot-",i,".png"), sep="") plot(time, get(i)) dev.off() }