R: Sampling from large pools

bigsample {ff} | R Documentation

## Sampling from large pools

### Description

`bigsample` samples quicker from large pools than `sample` does.

### Usage

    bigsample(x, ...)
    ## Default S3 method:
    bigsample(x, size, replace = FALSE, prob = NULL, negative = FALSE, ...)
    ## S3 method for class 'ff'
    bigsample(x, size, replace = FALSE, prob = NULL, ...)

### Arguments

`x` | the pool to sample from
`size` | the number of elements to sample
`replace` | TRUE to use sampling with replacement
`prob` | optional vector of sampling probabilities (recyled to pool length)
`negative` | `negative`
`...` | `...`

### Details

For small pools `sample` is called.

### Value

a vector of elements sampled from the pool (argument 'x')

### Note

Note that `bigsample` and `sample` do not necessarily return the same sequence of elements when `set.seed` is set before.

### Author(s)

Daniel Adler, Jens Oehlschlägel, Walter Zucchini

### See Also

`sample`, `ff`

### Examples

    message("Specify pool size")
    bigsample(1e8, 10)
    message("Sample ff elements (same as x[bigsample(length(ff(1:100 / 10)), 10)])")
    bigsample(ff(1:100 / 10), 10)
     ## Not run:
       message("Speed factor")
         (system.time(for(i in 1:10)sample(1e8, 10))[3]/10)
       / (system.time(for(i in 1:1000)bigsample(1e8, 10))[3]/1000)

    ## End(Not run)

[Package ff version 2.2-13 Index]