Accessing and changing list element attributes

Question

The background to this is that I'm mostly a Python programmer who has some passing familiarity with R. I've been tasked to look at an R script that was written by a Perl programmer who used for and while loops a lot, to see if I can make it more R-like and get it to run faster.

For example purposes, I have the following list:

> lnums <- list(1:5, 6:7, 8:12)

For the elements that have a length less than 5 (lnums[[2]]), I want to change the length to be 5. The original code uses a for loop to tack NA values to the end of any shorter vectors, and I know that there's got to be a better way than that. I was playing around with ways to get to it and came up with

> sapply(lnums, FUN=function(x) length(x) < 5)

which gets the right element, but I'm unable to figure out how to incorporate this into the subscript of a length(lnums[]) <- 5 statement. I know this is probably a really novice question, but I'd appreciate any help I can get.

Additionally, the reason that I want to increase the length of the shorter list elements is so that I can put the list into a data frame. It would be great if there was a way to do that without messing around with lengths, although I still wouldn't mind an answer to my first question to satisfy my curiosity if nothing else.

Thanks all. I've been digging through some topics in here and you've already helped me out quite a bit!

Answer 1

Here's one way:

lapply(lnums, 'length<-', 5)