R help - Apr 2011 - Hash table...

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....

cheers
Worik

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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?".

cu
	Philipp

-- 
Dr. Philipp Pagel
Lehrstuhl f?r Genomorientierte Bioinformatik
Technische Universit?t M?nchen
Wissenschaftszentrum Weihenstephan
Maximus-von-Imhof-Forum 3
85354 Freising, Germany
http://webclu.bio.wzw.tum.de/~pagel