[R] about subsetting vectors/list in R

[R. Michael Weylandt]

On Thu, Apr 4, 2013 at 7:55 PM, Abhishek Pratap <abhishek.vit at gmail.com> wrote:
> On Thu, Apr 4, 2013 at 5:53 PM, R. Michael Weylandt
> <michael.weylandt at gmail.com> wrote:
>> by_two <- function(x, collapse = ""){
>>    dim(x) <- c(length(x) / 2, 2)
>>    apply(x, 1, function(y) paste(y, collapse = collapse))
>> }
>
> Thanks.. just wondering if this will be slick for list/vectors with 100
> thousands of entries. ?

No, the apply() loop likely isn't optimal. But I can do

x <- rep(letters, length.out = 1e6)
system.time(by_two(x)) # Approx 15 seconds

on my slow old machine so this might be one of those cases of "good
enough and come worry about it if profiling shows its a real bottle
neck later".