My normal search foo is failing me. I'm trying to find an R function that returns ALL of the factors of an integer. There are at least 2 packages with factorize() functions: gmp and conf.design, however these functions return only prime factors. I'd like a function that returns all factors.
Obviously searching for this is made difficult since R has a construct called factors which puts a lot of noise in the search.
To follow up on my comment (thanks to @Ramnath for my typo), the brute force method seems to work reasonably well here on my 64 bit 8 gig machine:
FUN <- function(x) {
x <- as.integer(x)
div <- seq_len(abs(x))
factors <- div[x %% div == 0L]
factors <- list(neg = -factors, pos = factors)
return(factors)
}
A few examples:
> FUN(100)
$neg
[1] -1 -2 -4 -5 -10 -20 -25 -50 -100
$pos
[1] 1 2 4 5 10 20 25 50 100
> FUN(-42)
$neg
[1] -1 -2 -3 -6 -7 -14 -21 -42
$pos
[1] 1 2 3 6 7 14 21 42
#and big number
> system.time(FUN(1e8))
user system elapsed
1.95 0.18 2.14