Yes: $() has to calculate more on matching the names --- and is more
of a hack anyway.
Although, I would not worry to much about 0.3 seconds in 100
evaluations ...
Uwe
On 08.09.2010 14:31, Søren Højsgaard wrote:
Dear list
It seems to me that extracting elements from a list using '[[' is somewhat
faster than using '$'. 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 1:100) x[[21]] })
user system elapsed
0.550.000.54
system.time({ for (ii in 1:100) x[[u]]})
user system elapsed
0.840.000.84
system.time({ for (ii in 1:100) x$u})
user system elapsed
1.120.001.13
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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