On 11-04-14 4:48 AM, Philipp Pagel wrote:
On Thu, Apr 14, 2011 at 06:44:53PM +1200, Worik R wrote:
To improve the efficiency of a process I am writing I would like to cache
results. So I would like a data structure like a hash table.
So if I call Z<- f(Y) I can cache Z associated with Y: CACHE[Y]<- Z
I am stumped. I expected to be able to use a list for this but I cannot
figure how....
If y is an integer, factor or string you could try something along these
lines:
cache<- list()
y<- 12
cache[[as.character(y)]]<- sqrt(y)
y<-98
cache[[as.character(y)]]<- sqrt(y)
cache
$`12`
[1] 3.464102
$`98`
[1] 9.899495
Of course this can get you in trouble if y is a floating point
number because of the issues with "identity" of such numbers, as
discussed in ?all.equal and FAQ 7.31 "Why doesn't R think these
numbers are equal?".
I haven't actually done timing, but if there are likely to be a lot of y
values, I'd expect an environment created with hash=TRUE to be faster,
both in adding new items and in retrieving existing ones. The code is
pretty similar:
Use
cache <- new.env(hash=TRUE)
to create it, and
ls(cache)
to list the names, or
as.list(cache)
to print it as a list. Other than that, the assignment and retrieval
code is identical.
Duncan Murdoch
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
