Boris, You may want to look into the R6 package. This package has tools that help create objects (environments) with methods that can use and change the object. You can have your persistent table stored as part of your object and then create methods that will use and modify the table within the object.
On Sat, Mar 19, 2016 at 10:45 AM, Boris Steipe <boris.ste...@utoronto.ca> wrote: > Dear all - > > I need to have a function maintain a persistent lookup table of results for > an expensive calculation, a named vector or hash. I know that I can just keep > the table in the global environment. One problem with this approach is that > the function should be able to delete/recalculate the table and I don't like > side-effects in the global environment. This table really should be private. > What I don't know is: > -A- how can I keep the table in an environment that is private to the > function but persistent for the session? > -B- how can I store and reload such table? > -C- most importantly: is that the right strategy to initialize and maintain > state in a function in the first place? > > > For illustration ... > > ----------------------------------- > > myDist <- function(a, b) { > # retrieve or calculate distances > if (!exists("Vals")) { > Vals <<- numeric() # the lookup table for distance values > # here, created in the global env. > } > key <- sprintf("X%d.%d", a, b) > thisDist <- Vals[key] > if (is.na(thisDist)) { # Hasn't been calculated yet ... > cat("Calculating ... ") > thisDist <- sqrt(a^2 + b^2) # calculate with some expensive function > ... > Vals[key] <<- thisDist # store in global table > } > return(thisDist) > } > > > # run this > set.seed(112358) > > for (i in 1:10) { > x <- sample(1:3, 2) > print(sprintf("d(%d, %d) = %f", x[1], x[2], myDist(x[1], x[2]))) > } > > > Thanks! > Boris > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. -- Gregory (Greg) L. Snow Ph.D. 538...@gmail.com ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.