R: Reading and writing vectors (low-level)

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()

[Package ff version 2.2-13 Index]