Evaluates an R expression with memoization

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.

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

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.

Value

Returns the value of the evaluated expr expression, if any.

Author

Henrik Bengtsson

See also

Internally, eval() is used to evaluate the expression.

Examples

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


## 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 ...)
#> 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

## 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