bigsample: Sampling from large pools

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

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)

ff documentation built on Feb. 16, 2023, 7:48 p.m.