ff: ffsort – R documentation

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ffsort

Sorting of ff vectors

Description

Sorting: sort an ff vector – optionally in-place

Usage

ffsort(x
, aux = NULL
, has.na = TRUE
, na.last = TRUE
, decreasing = FALSE
, inplace = FALSE
, decorate = FALSE
, BATCHBYTES = getOption("ffmaxbytes")
, VERBOSE = FALSE
)

Arguments

`x`	an ff vector
`aux`	NULL or an ff vector of the same type for temporary storage
`has.na`	boolean scalar telling ffsort whether the vector might contain `NA`s. Note that you risk a crash if there are unexpected `NA`s with `has.na=FALSE`
`na.last`	boolean scalar telling ffsort whether to sort `NA`s last or first. Note that 'boolean' means that there is no third option `NA` as in `sort`
`decreasing`	boolean scalar telling ffsort whether to sort increasing or decreasing
`inplace`	boolean scalar telling ffsort whether to sort the original ff vector (`TRUE`) or to create a sorted copy (`FALSE`, the default)
`decorate`	boolean scalar telling ffsort whether to decorate the returned ff vector with `is.sorted` and `na.count` attributes.
`BATCHBYTES`	maximum number of RAM bytes ffsort should try not to exceed
`VERBOSE`	cat some info about the sorting

Details

ffsort tries to sort the vector in-RAM respecting the BATCHBYTES limit. If a fast sort it not possible, it uses a slower in-place sort (shellsort). If in-RAM is not possible, it uses (a yet simple) out-of-memory algorithm. Like ramsort the in-RAM sorting method is choosen depending on context information. If a key-index sort can be used, ffsort completely avoids merging disk based subsorts. If argument decorate=TRUE is used, then na.count(x) will return the number of NAs and is.sorted(x) will return TRUE if the sort was done with na.last=TRUE and decreasing=FALSE.

Value

An ff vector – optionally decorated with is.sorted and na.count, see argument 'decorate'

Note

the ff vector may not have a names attribute

Author(s)

Jens Oehlschlägel

Examples

n <- 1e6
   x <- ff(c(NA, 999999:1), vmode="double", length=n)
   x <- ffsort(x)
   x
   is.sorted(x)
   na.count(x)
   x <- ffsort(x, decorate=TRUE)
   is.sorted(x)
   na.count(x)
   x <- ffsort(x, BATCHBYTES=n, VERBOSE=TRUE)

ff

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

v4.0.4

GPL-2 | GPL-3 | file LICENSE

Authors

Daniel Adler [aut], Christian Gläser [aut], Oleg Nenadic [aut], Jens Oehlschlägel [aut, cre], Martijn Schuemie [aut], Walter Zucchini [aut]

Initial release

2020-10-13