Question

Possible Duplicate:
How to name variables on the fly in R?

I have 10 objects of type list named: list1, list2, …, list10. And I wanted to use the output from my function FUN to replace the first index of these list variables through a for loop like this:

for (i in 1:10){
  eval(parse(test=(paste("list",i,sep=""))))[[1]] <- FUN()
}

but this does not work. I also used lapply in this way and again it is wrong:

 lapply(eval(parse(text=(paste("list",i,sep=""))))[[1]], FUN)

Any opinion would be appreciated.

Answer 1

This is FAQ 7.21. The most important part of that FAQ is the last part that says not to do it that way, but to put everything into a list and operate on the list.

You can put your objects into a list using code like:

mylists <- lapply( 1:10, function(i) get( paste0('list',i) ) )

Then you can do the replacement with code like:

mylists <- lapply( mylists, function(x) { x[[1]] <- FUN()
  x} )

Now if you want to save all the lists, or delete all the lists, you just have a single object that you need to work with instead of looping through the names again. If you want to do something else to each list then you just use lapply or sapply on the overall list in a single easy step without worrying about the loop. You can name the elements of the list to match the original names if you want and access them that way as well. Keeping everything of interest in a single list will also make your code safer, much less likely to accidentilly overwrite or delete another object.