On 12/30/2010 02:30 PM, Paul Rigor wrote:
> Thanks gang,
> I'll work with named vectors and concatenate as needed.
This might be ok for small problems, but concatenation is an inefficient
R pattern -- the objects being concatenated are copied in full, so
becomes longer, and the concatenation slower, with each new key. With
a <- integer(); t0 <- Sys.time()
for (i in seq_len(1e6)) {
a <- c(a, i)
if (0 == i %% 10000)
print(i / as.numeric(Sys.time() - t0))
}
we have, in 'appends per second'
[1] 3236.76
[1] 2425.111
[1] 1757.52
[1] 1331.846
We don't really have a dictionary here, either, as the 'key' values are
not stored. Phil's suggest suffers from the same type of issue, where
the addition of new keys implies growing (reallocating) the vector.
a <- integer(); t0 <- Sys.time()
for (i in seq_len(1e6)) {
key <- as.character(i)
a[[key]] <- i
if (0 == i %% 10000)
print(i / as.numeric(Sys.time() - t0))
}
[1] 12659.18
[1] 9516.288
[1] 6821.47
[1] 5907.782
Better to use an environment (and live with reference semantics)
e <- new.env(parent=emptyenv()); t0 <- Sys.time()
for (i in seq_len(1e6)) {
key <- as.character(i)
e[[key]] <- i
if (0 == i %% 10000)
print(i / as.numeric(Sys.time() - t0))
}
with
[1] 20916.56
[1] 21421.85
[1] 21762.04
[1] 21207.69
[1] 21239.19
The usual alternative to the concatenation pattern is
'pre-allocate-and-fill'
x <- integer(1e6); t0 <- Sys.time()
for (i in seq_len(1e6)) {
???
}
but this doesn't work with key/value pairs because there is no sense (or
is there?) in which the keys can be 'pre-allocated'.
Creating the dictionary in one go is very efficient
> system.time(d <-
+ structure(seq_len(1e6), .Names=as.character(seq_len(1e6))))
user system elapsed
0.417 0.002 0.419
Martin
> Paul
>
> On Thu, Dec 23, 2010 at 7:39 AM, Seth Falcon <s...@userprimary.net
> <mailto:s...@userprimary.net>> wrote:
>
> On Wed, Dec 22, 2010 at 7:05 PM, Martin Morgan <mtmor...@fhcrc.org
> <mailto:mtmor...@fhcrc.org>> wrote:
> > On 12/22/2010 05:49 PM, Paul Rigor wrote:
> >> Hi,
> >>
> >> I was wondering if anyone has played around this this package called
> >> "rdict"? It attempts to implement a hash table in R using skip
> lists. Just
> >> came across it while trying to look for simpler text manipulation
> methods:
> >>
> >>
> http://userprimary.net/posts/2010/05/29/rdict-skip-list-hash-table-for-R/
> >
> > kind of an odd question, so kind of an odd answer.
> >
> > I'd say this was an implementation of skip lists in C with an R
> > interface.
>
> I had to play around with the rdict package in order to write it, but
> haven't used it much since :-P
> Be sure to look at R's native environment objects which provide a hash
> table structure and are suitable for many uses.
>
> + seth
>
> --
> Seth Falcon | @sfalcon | http://userprimary.net/
>
>
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