physical.ffdf: Getting physical and virtual attributes of ffdf objects

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

Getting physical and virtual attributes of ffdf objects

Description

Functions for getting physical and virtual attributes of ffdf objects.

Usage

## S3 method for class 'ffdf'
physical(x)
## S3 method for class 'ffdf'
virtual(x)

Arguments

x	an ffdf object

Details

ffdf objects enjoy a complete decoupling of virtual behaviour from physical storage. The physical component is simply a (potentially named) list where each element represents an atomic ff vector or matrix. The virtual component is itself a dataframe, each row of which defines a column of the ffdf through a mapping to the physical component.

Value

'physical.ffdf' returns a list with atomic ff objects.
'virtual.ffdf' returns a data.frame with the following columns

VirtualVmode	the vmode of this row (=ffdf column)
AsIs	logical defining the AsIs status of this row (=ffdf column)
VirtualIsMatrix	logical defining whether this row (=ffdf column) represents a matrix
PhysicalIsMatrix	logical reporting whether the corresponding physical element is a matrix
PhysicalElementNo	integer identifying the corresponding physical element
PhysicalFirstCol	integer identifying the first column of the corresponding physical element (1 if it is not a matrix)
PhysicalLastCol	integer identifying the last column of the corresponding physical element (1 if it is not a matrix)

Author(s)

Jens Oehlschlägel

See Also

ffdf, physical, virtual, vmode

Examples

  x <- 1:2
  y <- matrix(1:4, 2, 2)
  z <- matrix(1:4, 2, 2)

  message("Here the y matrix is first converted to single columns by data.frame, 
then those columns become ff")
  d <- as.ffdf(data.frame(x=x, y=y, z=I(z)))
  physical(d)
  virtual(d)

  message("Here the y matrix is first converted to ff, and then stored still as matrix 
in the ffdf object (although virtually treated as columns of ffdf)")
  d <- ffdf(x=as.ff(x), y=as.ff(y), z=I(as.ff(z)))
  physical(d)
  virtual(d)

  message("Apply the usual methods extracting physical attributes")
  lapply(physical(d), filename)
  lapply(physical(d), vmode)
  message("And don't confuse with virtual vmode")
  vmode(d)

  rm(d); gc()

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