OK, we're all familiar with double colon operator in R. Whenever I'm about to write some function, I use require(<pkgname>), but I was always thinking about using :: instead. Using require in custom functions is better practice than library, since require returns warning and FALSE, unlike library, which returns error if you provide a name of non-existent package.
On the other hand, :: operator gets the variable from the package, while require loads whole package (at least I hope so), so speed differences came first to my mind. :: must be faster than require.
And I did some analysis in order to check that - I've written two simple functions that load read.systat function from foreign package, with require and :: respectively, hence import Iris.syd dataset that ships with foreign package, replicated functions 1000 times each (which was shamelessly arbitrary), and... crunched some numbers.
Strangely (or not) I found significant differences in terms of user CPU and elapsed time, while there were no significant differences in terms of system CPU. And yet more strange conclusion: :: is actually slower! Documentation for :: is very blunt, and just by looking at sources it's obvious that :: should perform better!
require
#!/usr/local/bin/r
## with require
fn1 <- function() {
require(foreign)
read.systat("Iris.syd", to.data.frame=TRUE)
}
## times
n <- 1e3
sink("require.txt")
print(t(replicate(n, system.time(fn1()))))
sink()
double colon
#!/usr/local/bin/r
## with ::
fn2 <- function() {
foreign::read.systat("Iris.syd", to.data.frame=TRUE)
}
## times
n <- 1e3
sink("double_co