readwrite.ff: Reading and writing vectors (low-level)

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

Reading and writing vectors (low-level)

Description

Simpe low-level interface for reading and writing vectors from ff files.

Usage

read.ff(x, i, n)
write.ff(x, i, value, add = FALSE)
readwrite.ff(x, i, value, add = FALSE)

Arguments

x	an ff object
i	a start position in the ff file
n	number of elements to read
value	vector of elements to write
add	TRUE if the values should rather increment than overwrite at the target positions

Details

readwrite.ff combines the effects of read.ff and write.ff in a single operation: it retrieves the old values starting from position i before changing them. getset.ff will maintain na.count.

Value

read.ff returns a vector of values, write.ff returns the 'changed' ff object (like all assignment functions do) and readwrite.ff returns the values at the target position. More precisely readwrite.ff(x, i, value, add=FALSE) returns the old values at the position i while readwrite.ff(x, i, value, add=TRUE) returns the incremented values of x.

Note

read.ff, write.ff and readwrite.ff are low level functions that do not support ramclass and ramattribs and thus will not give the expected result with factor and POSIXct

Author(s)

Jens Oehlschlägel

See Also

getset.ff for low-level scalar access and [.ff for high-level access

Examples

  x <- ff(0, length=12)
  read.ff(x, 3, 6)
  write.ff(x, 3, rep(1, 6))
  x
  write.ff(x, 3, rep(1, 6), add=TRUE)
  x
  readwrite.ff(x, 3, rep(1, 6), add=TRUE)
  readwrite.ff(x, 3, rep(1, 6))
  x
  rm(x); gc()

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