memento: Remembers and outputs the result of a slow function

In StratigrapheR: Integrated Stratigraphy

Remembers and outputs the result of a slow function

Description

Memento mori; you do not have time to lose on unnecessary calculations. This function remembers the output of a slow function, for given arguments and, if asked politely, given files and a given random seed. If they match the previous arguments, files and seeds, the output is provided without delay, otherwise the function runs, and all the parameters are saved for next time. The trade-off is to assign a folder to store the data (see also details). The function can also be forced to rerun.

Usage

memento(
  what,
  args,
  name,
  dir = getwd(),
  subdir = "memento",
  rerun = F,
  check.files = list(),
  files.dir = getwd(),
  check.seed = F,
  speak = T
)

Arguments

what	a (slow) function
args	a list of the the arguments to give to the function. If they differ from saved values, the function will run again.
name	the name of the folder where to store the info. THIS NEEDS TO BE DIFFERENT FOR EACH IMPLEMENTATION OF THE FUNCTION IN IDENTICAL DIRECTORIES.
dir	the directory. You can set it as the working directory via getwd.
subdir	a name for a subdirectory (useful when the function is used several time in a script)
rerun	if TRUE, the function is rerun no matter what. This is useful to update information that is not present in the R environment, for instance if you load data from external files that have been updated.
check.files	a list of files to check changes in (see details). If the list is of length 0, no file is checked.
files.dir	directory for teh files to be checked.
check.seed	if TRUE, the value of the random seed in effect will be taken into account; if it changes, the function will run again.
speak	whether to signify when the (slow) function is running

Details

file data is summarized using MD5sum, which can have limitations in data size (2^64 bits) and in cryptographic purposes.

Value

the output of the function

Examples

tf <- tempdir()
if(exists("run.number")) run.number <- run.number + 1 else run.number <-  1
name <- paste("T",run.number)

testfun <- function(a = 1, time = 3){

  Sys.sleep(time)

  return(a  + 0.1 * abs(rnorm(1)))

}

# First time running; the function takes some time, memento needs the
# output to be generated, and will remember for later.
set.seed(43)
memento(testfun,  args = list(a = 7), name = name, dir = tf)

set.seed(43)
testfun(7, time = 0)

# Second time running: memento directly outputs the remembered results.
# In this case, the seed is ignored, so the result is different from what
# would be obtained with a different seed
set.seed(45)
memento(testfun,  args = list(a = 7), name = name, dir = tf)

set.seed(45)
testfun(7, time = 0)

# First time running while taking into account the random seed;
# the function takes some time to generate the result
set.seed(42)
memento(testfun,  args = list(a = 7), name = name, dir = tf, check.seed = TRUE)

# Second time running with an identical random seed;
# memento directly outputs the results
set.seed(42)
memento(testfun,  args = list(a = 7), name = name, dir = tf, check.seed = TRUE)

# The seed is changed: the result is computed anew
set.seed(47)
memento(testfun,  args = list(a = 7), name = name, dir = tf, check.seed = TRUE)

StratigrapheR documentation built on July 9, 2023, 6:02 p.m.