cache_name {onlineforecast}

Generation of a name for a cache file for the value of a function.

Description

Caching of the value returned by a function

Usage

cache_name(..., cachedir = "cache")

Arguments

...

The objects from which to calculate cache file name. If no objects given, then all the objects of the calling function are used for generating the checksum for the file name.

cachedir

Path for saving the cache, i.e. prefixed to the generated name, remember to end with '/' to make a directory.

Details

Use it in the beginning of a function, which runs a time consuming calculation, like fitting a model using optimization.

It makes a cache name, which can be used to save a unique cache file (see cache_save()).

The cache_name function must receive all the objects (in ...) which influence the value of the function. It simply calculates a checksum using the digest package.

Further, it finds the name of the calling function and its definition, such that if anything changes in the function definition, then the cache file name changes too.

Value

A generated cache file name.

Examples

# A function for demonstrating the using caching
fun <- function(x, y){
    # Generate the cache name (no argument given, so both x and y is used)
    nm <- cache_name(cachedir=cachedir)
    # If the result is cached, then just return it
    if(file.exists(nm)){ return(readRDS(nm)) }
    # Do the calculation
    res <- x^2 + y + 1
    # Wait 1 sec
    Sys.sleep(1)
    # Save for cache
    cache_save(res, nm)
    # Return
    return(res)
}

# For this example use a temporary directory 
# In real use this should not be temporary! (changes between R sessions with tempdir())
cachedir <- tempdir()

# Uncomment to run:
# First time it takes at least 1 sec.
#fun(x=2,y=2)
# Second time it loads the cache and is much faster
#fun(x=2,y=2)
# Try changing the arguments (x,y) and run again

# See the cache file(s)
#dir(cachedir)
# Delete the cache folder
#unlink(cachedir, recursive=TRUE)

# Demonstrate how cache_name() is functioning
# Cache using the all objects given in the function calling, i.e. both x and y
fun <- function(x,y){
    x^2 + y + 1
    return(cache_name())
}
# These are the same (same values)
fun(x=1,y=2)
fun(1,2)
fun(y=2,x=1)
# But this one is different
fun(x=2,y=1)

# Test: cache using the values specified in the cache_name call
fun2 <- function(x,y){
    x^2 + y + 1
    return(cache_name(x))
}

# So now its only the x value that change the name
fun2(1,2)
fun2(1,3)
# But this one is different 
fun2(3,3)
# And the function named changed the name