evalWithMemoization: Evaluates an R expression with memoization

Description

Evaluates an R expression with memoization such that the same objects are assigned to the current environment and the same result is returned, if any.

Usage

evalWithMemoization(expr, key=NULL, ..., envir=parent.frame(),
  drop=c("srcref", "srcfile", "wholeSrcref"), force=FALSE)

Value

Returns the value of the evaluated expr

expression, if any.

Arguments

expr: The expression to be evaluated.
key: Additional objects to uniquely identify the evaluation.
...: Additional arguments passed to loadCache() and saveCache().
envir: The environment in which the expression should be evaluated.
drop: character vector of expr attributes to drop. The default is to drop all source-reference information.
force: If TRUE, existing cached results are ignored.

Author

Henrik Bengtsson

Examples

Run this code

for (kk in 1:5) {
  cat(sprintf("Iteration #%d:\n", kk))
  res <- evalWithMemoization({
    cat("Evaluating expression...")
    a <- 1
    b <- 2
    c <- 4
    Sys.sleep(1)
    cat("done\n")
    b
  })
  print(res)

  # Sanity checks
  stopifnot(a == 1 && b == 2 && c == 4)

  # Clean up
  rm(a, b, c)
} # for (kk ...)


## OUTPUTS:
## Iteration #1:
## Evaluating expression...done
## [1] 2
## Iteration #2:
## [1] 2
## Iteration #3:
## [1] 2
## Iteration #4:
## [1] 2
## Iteration #5:
## [1] 2


############################################################
# WARNING
############################################################
# If the expression being evaluated depends on
# "input" objects, then these must be be specified
# explicitly as "key" objects.
for (ii in 1:2) {
  for (kk in 1:3) {
    cat(sprintf("Iteration #%d:\n", kk))
    res <- evalWithMemoization({
      cat("Evaluating expression...")
      a <- kk
      Sys.sleep(1)
      cat("done\n")
      a
    }, key=list(kk=kk))
    print(res)

    # Sanity checks
    stopifnot(a == kk)

    # Clean up
    rm(a)
  } # for (kk ...)
} # for (ii ...)

## OUTPUTS:
## Iteration #1:
## Evaluating expression...done
## [1] 1
## Iteration #2:
## Evaluating expression...done
## [1] 2
## Iteration #3:
## Evaluating expression...done
## [1] 3
## Iteration #1:
## [1] 1
## Iteration #2:
## [1] 2
## Iteration #3:
## [1] 3