ffwhich: Create an index from a filter statement

In ffbase: Basic Statistical Functions for Package 'ff'

Description

ffwhich creates an ff integer index vector from a filter expression. The resulting vector can be used to index or subset a ffdf or ff vector.

Usage

ffwhich(x, expr, ...)

Arguments

x	ff or ffdf object
expr	R code that evaluates to a logical
...	not used

See Also

ffindexget ffindexset

Examples

# create a ff vector
x <- ff(10:1)
# make an ff index vector
idx <- ffwhich(x, x < 5)
# use it to retrieve values from x
x[idx][]

# create a ffdf data.frame
dat <- ffdf(x1=x, y1=x)
# create an ff index vector from a filter statement
idx <- ffwhich(dat, x1 < 5 & y1 > 2)
# use it to select data from the data.frame
dat[idx,][,]

Example output

Loading required package: ff
Loading required package: bit
Attaching package bit
package:bit (c) 2008-2012 Jens Oehlschlaegel (GPL-2)
creators: bit bitwhich
coercion: as.logical as.integer as.bit as.bitwhich which
operator: ! & | xor != ==
querying: print length any all min max range sum summary
bit access: length<- [ [<- [[ [[<-
for more help type ?bit

Attaching package: 'bit'

The following object is masked from 'package:base':

    xor

Attaching package ff
- getOption("fftempdir")=="/work/tmp/tmp/RtmpsTm6Ce"

- getOption("ffextension")=="ff"

- getOption("ffdrop")==TRUE

- getOption("fffinonexit")==TRUE

- getOption("ffpagesize")==65536

- getOption("ffcaching")=="mmnoflush"  -- consider "ffeachflush" if your system stalls on large writes

- getOption("ffbatchbytes")==16777216 -- consider a different value for tuning your system

- getOption("ffmaxbytes")==536870912 -- consider a different value for tuning your system


Attaching package: 'ff'

The following objects are masked from 'package:bit':

    clone, clone.default, clone.list

The following objects are masked from 'package:utils':

    write.csv, write.csv2

The following objects are masked from 'package:base':

    is.factor, is.ordered


Attaching package: 'ffbase'

The following objects are masked from 'package:ff':

    [.ff, [.ffdf, [<-.ff, [<-.ffdf

The following objects are masked from 'package:base':

    %in%, table

[1] 4 3 2 1
  x1 y1
1  4  4
2  3  3

ffbase documentation built on Feb. 27, 2021, 5:06 p.m.