Getting and setting length

Gets and sets length of ff objects.

# S3 method for class 'ff'
length(x)
# S3 method for class 'ff'
length(x) <- value

Arguments

x

object to query

value

new object length

Details

Changing the length of ff objects is only allowed if no vw is used. Changing the length of ff objects will remove any dim.ff and dimnames.ff attribute. Changing the length of ff objects will remove any na.count or is.sorted attribute and warn about this. New elements are usually zero, but it may depend on OS and filesystem what they really are. If you want standard R behaviour: filling with NA ,you need to do this yourself. As an exception to this rule, ff objects with names.ff will be filled with NA's automatically, and the length of the names will be adjusted (filled with position numbers where needed, which can easily consume a lot of RAM, therefore removing 'names' will help to faster increase length without RAM problems).

Note

Special care needs to be taken with regard ff objects that represent factors. For ff factors based on UNSIGNED vmodes, new values of zero are silently interpreted as the first factor level. For ff factors based on SIGNED vmodes, new values of zero result in illegal factor levels. See nrow<-.

Value

Integer scalar

Author

Jens Oehlschlägel

See also

length, maxlength, file.resize, dim, virtual

Examples

  x <- ff(1:12)
  maxlength(x)
#> [1] 12
  length(x)
#> [1] 12
  length(x) <- 10
  maxlength(x)
#> [1] 10
  length(x)
#> [1] 10
  length(x) <- 16
  maxlength(x)
#> [1] 16
  length(x)
#> [1] 16
  rm(x); gc()
#>           used (Mb) gc trigger  (Mb) max used  (Mb)
#> Ncells 1160835 62.0    1994352 106.6  1994352 106.6
#> Vcells 2162599 16.5    8790397  67.1  8790397  67.1