Demo of the bit package

In bit: Classes and Methods for Fast Memory-Efficient Boolean Selections

knitr::opts_chunk$set(collapse = TRUE, comment = "#>")
require(bit)
.ff.version <- try(packageVersion("ff"), silent = TRUE)
.ff.is.available <- !inherits(.ff.version, "try-error") && .ff.version >= "4.0.0" && require(ff)
#tools::buildVignette("vignettes/bit-demo.Rmd")
#devtools::build_vignettes()

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bit type

Create a huge boolean vector (no NAs allowed)

n <- 1e8
b1 <- bit(n)
b1

It costs only one bit per element

object.size(b1)/n

A couple of standard methods work

b1[10:30] <- TRUE
summary(b1)

Create a another boolean vector with TRUE in some different positions

b2 <- bit(n)
b2[20:40] <- TRUE
b2

fast boolean operations

b1 & b2

fast boolean operations

summary(b1 & b2)

bitwhich type

Since we have a very skewed distribution we may coerce to an even sparser representation

w1 <- as.bitwhich(b1) 
w2 <- as.bitwhich(b2)
object.size(w1)/n

and everything

w1 & w2

works as expected

summary(w1 & w2)

even mixing

summary(b1 & w2)

processing chunks

Many bit functions support a range restriction,

summary(b1, range=c(1,1000))

which is useful

as.which(b1, range=c(1, 1000))

for filtered chunked looping

lapply(chunk(from=1, to=n, length=10), function(i)as.which(b1, range=i))

over large ff vectors

options(ffbatchbytes=1024^3)
x <- ff(vmode="single", length=n)
x[1:1000] <- runif(1000)
lapply(chunk(x, length.out = 10), function(i)sum(x[as.hi(b1, range=i)]))

and wrap-up

delete(x)
rm(x, b1, b2, w1, w2, n)

for more info check the usage vignette

bit documentation built on Nov. 16, 2022, 1:12 a.m.