Dear list
It seems to me that extracting elements from a list using '[[' is somewhat
faster than using '$'. For example:
> x <- as.list(1:25)
> names(x) <- letters[1:length(x)]
> dput(x)
structure(list(a = 1L, b = 2L, c = 3L, d = 4L, e = 5L, f = 6L,
g = 7L, h = 8L, i = 9L, j = 10L, k = 11L, l = 12L, m = 13L,
n = 14L, o = 15L, p = 16L, q = 17L, r = 18L, s = 19L, t = 20L,
u = 21L, v = 22L, w = 23L, x = 24L, y = 25L), .Names = c("a",
"b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n",
"o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y"))
>
> system.time({ for (ii in 1:1000000) x[[21]] })
user system elapsed
0.55 0.00 0.54
> system.time({ for (ii in 1:1000000) x[["u"]]})
user system elapsed
0.84 0.00 0.84
> system.time({ for (ii in 1:1000000) x$u})
user system elapsed
1.12 0.00 1.13
Does anyone know if this is always the case? (I have not found anything about
speed in this connection on the help pages, apologies if I have overlooked
something).
I use R.2.11.1 on Windows 7.
Regards
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