readwrite.ff {ff} | R Documentation |
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()