R: Getting physical and virtual attributes of ffdf objects

physical.ffdf {ff} | R Documentation

## 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()

[Package ff version 2.2-13 Index]