getset.ff: Reading and writing vectors of values (low-level)

In kindlychung/ff: memory-efficient storage of large data on disk and fast access functions

Description

The three functions get.ff, set.ff and getset.ff provide the simplest interface to access an ff file: getting and setting vector of values identified by positive subscripts

Usage

get.ff(x, i)
set.ff(x, i, value, add = FALSE)
getset.ff(x, i, value, add = FALSE)

Arguments

x	an ff object
i	an index position within the ff file
value	the value to write to position i
add	TRUE if the value should rather increment than overwrite at the index position

Details

getset.ff combines the effects of get.ff and set.ff in a single operation: it retrieves the old value at position i before changing it. getset.ff will maintain na.count.

Value

get.ff returns a vector, set.ff returns the 'changed' ff object (like all assignment functions do) and getset.ff returns the value at the subscript positions. More precisely getset.ff(x, i, value, add=FALSE) returns the old values at the subscript positions i while getset.ff(x, i, value, add=TRUE) returns the incremented values at the subscript positions.

Note

get.ff, set.ff and getset.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 Oehlschl<c3><a4>gel

See Also

readwrite.ff for low-level access to contiguous chunks and [.ff for high-level access

Examples

 x <- ff(0, length=12)
 get.ff(x, 3L)
 set.ff(x, 3L, 1)
 x
 set.ff(x, 3L, 1, add=TRUE)
 x
 getset.ff(x, 3L, 1, add=TRUE)
 getset.ff(x, 3L, 1)
 x
 rm(x); gc()

kindlychung/ff documentation built on May 20, 2019, 9:58 a.m.