zipper

it zips the index in the basket!

Zips two sorted arrays into each other. That's it. Not for CRAN.

-- Steven E. Pav, shabbychef@gmail.com

Installation

This package can be installed via drat, or from github:

# via drat:
if (require(drat)) {
    drat:::add("shabbychef")
    install.packages("zipper")
}
# get snapshot from github (may be buggy)
if (require(devtools)) {
    # install_github("shabbychef/zipper")
install.packages("zipper", repos = c('https://shabbychef.r-universe.dev', 'https://cloud.r-project.org'))
}

What?

Suppose you have two sorted arrays and need to align them. That's a zip operation. Back when I worked with time series (in Matlab), a zip operation was at the base of the 'look back' join operation. That is all this package does:

require(zipper)
set.seed(1234)
reference_x <- sort(rnorm(10000))
lookup_y <- sort(rnorm(100))
idxs <- zipper::zip_le(reference_x, lookup_y)
head(idxs)

## [1] 104 106 119 126 155 165

# compare to this slow version:
altv <- rep(NA_integer_, length(lookup_y))
for (iii in seq_along(lookup_y)) {
    altv[iii] <- sum(reference_x <= lookup_y[iii])
}
stopifnot(all.equal(altv, idxs))