Update ff content from another object

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

# 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.

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.

Value

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

Author

Jens Oehlschlägel

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.")
#> 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
#> ff (open) integer length=100 (100)
#>   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8]        [93]  [94]  [95]  [96] 
#>    -1    -2    -3    -4    -5    -6    -7    -8     :   -93   -94   -95   -96 
#>  [97]  [98]  [99] [100] 
#>   -97   -98   -99  -100 
  y
#> ff (open) integer length=100 (100)
#>   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8]        [93]  [94]  [95]  [96] 
#>    -1    -2    -3    -4    -5    -6    -7    -8     :   -93   -94   -95   -96 
#>  [97]  [98]  [99] [100] 
#>   -97   -98   -99  -100 
  x[] <- 1:100
  x <- update(x, from=y, delete=NA)
  x
#> ff (open) integer length=100 (100)
#>   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8]        [93]  [94]  [95]  [96] 
#>    -1    -2    -3    -4    -5    -6    -7    -8     :   -93   -94   -95   -96 
#>  [97]  [98]  [99] [100] 
#>   -97   -98   -99  -100 
  y
#> ff (open) integer length=100 (100)
#>   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8]        [93]  [94]  [95]  [96] 
#>     1     2     3     4     5     6     7     8     :    93    94    95    96 
#>  [97]  [98]  [99] [100] 
#>    97    98    99   100 
  x <- update(x, from=y, delete=TRUE)
  x
#> ff (open) integer length=100 (100)
#>   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8]        [93]  [94]  [95]  [96] 
#>     1     2     3     4     5     6     7     8     :    93    94    95    96 
#>  [97]  [98]  [99] [100] 
#>    97    98    99   100 
  y
#> ff (deleted) integer length=100 (100)
  x
#> ff (open) integer length=100 (100)
#>   [1]   [2]   [3]   [4]   [5]   [6]   [7]   [8]        [93]  [94]  [95]  [96] 
#>     1     2     3     4     5     6     7     8     :    93    94    95    96 
#>  [97]  [98]  [99] [100] 
#>    97    98    99   100 
  rm(x,y); gc()
#>           used (Mb) gc trigger  (Mb) max used  (Mb)
#> Ncells 1181890 63.2    1994352 106.6  1994352 106.6
#> Vcells 2206090 16.9    8790397  67.1  8790397  67.1

  if (FALSE) { # \dontrun{
    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()
  } # }