update.ff: Update ff content from another object

In ff: Memory-Efficient Storage of Large Data on Disk and Fast Access Functions

Update ff content from another object

Description

update copies updates one ff object with the content of another object.

Usage

## S3 method for class 'ff'
update(object, from, delete = FALSE, bydim = NULL, fromdim = NULL
, BATCHSIZE = .Machine$integer.max, BATCHBYTES = getOption("ffbatchbytes")
, VERBOSE = FALSE, ...)
## S3 method for class 'ffdf'
update(object, from, ...)

Arguments

object	an ff object to which to update
from	an object from which to uodate
delete	NA for quick update with file-exchange, TRUE for quick update with deleting the 'from' object after the update, can speed up updating significantly
bydim	how to interpret the content of the object, see ff
fromdim	how to interpret the content of the 'from' object, see ff
BATCHSIZE	BATCHSIZE
BATCHBYTES	BATCHBYTES
VERBOSE	VERBOSE
...	further arguments

Details

If the source object is.ff and not delete=FALSE then instead of slow copying we - if possible - try to swap and rename the files behind the ff objects. Quick update requires that the two ff objects are vectorCompatible, that both don't use vw, that they have identical maxlength and identical levels.ff.

Value

An ff object like the input 'object' updated with the content of the 'from' object.

Note

You don't have a guarantee that with delete=TRUE the 'from' object gets deleted or with delete=NA the 'from' objects carries the content of 'object'. Such expectations only turn true if really a quick update was possible.

Author(s)

Jens Oehlschlägel

See Also

ff, clone, ffvecapply, vectorCompatible, filename

Examples

  x <- ff(1:100)
  y <- ff(-(1:100))
  message("You should make it a habit to re-assign the return value 
of update although this is not needed currently.")
  x <- update(x, from=y)
  x
  y
  x[] <- 1:100
  x <- update(x, from=y, delete=NA)
  x
  y
  x <- update(x, from=y, delete=TRUE)
  x
  y
  x
  rm(x,y); gc()

  ## Not run: 
    message("timings")
    x <- ff(1:10000000)
    y <- ff(-(1:10000000))
    system.time(update(x, from=y))
    system.time(update(y, from=x, delete=NA))
    system.time(update(x, from=y, delete=TRUE))
    rm(x,y); gc()
  
## End(Not run)

ff documentation built on Sept. 30, 2024, 9:38 a.m.