In egnha/dub: Unpacking Assignment for Lists via Pattern Matching

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  fig.path = "man/figures/README-",
  out.width = "100%"
)

dub

dub is a small, single-purpose R package for unpacking assignment: it provides an operator %<<-% that enables you to assign (nested) components of a list (or vector) to names via pattern matching. The pattern matching syntax mirrors the semantics of list(). Think of the “dub(ble) arrow” <<- as a pictograph representing multiple <-'s.

library(dub)

(one : two : three) %<<-% 1:3
one
two
three

(x) %<<-% list(list("x"))
((y)) %<<-% list(list("y"))
x
y

(u : (v : w)) %<<-% list(1, list(2, 3:4))
u
v
w

# Use . to drop specific components, ... to drop greedily (the _ in Haskell)
(. : width : ... : species) %<<-% iris
head(width)
head(species)

More details and examples are in the package documentation (?`%<<-%`).

Installation

Install from CRAN:

``````r install.packages("dub")

Alternatively, install the development version from GitHub:

```r
# install.packages("devtools")
devtools::install_github("egnha/dub")

Prior art

Unpacking/multiple assignment appears in other languages (e.g., Python, JavaScript, Clojure). While R has no such feature, using a custom operator to do this has long been a folklore method. To my knowledge, the earliest implementation is by Gabor Grothendieck (2004), cf. list in the gsubfn package.

If you need specialized forms of "destructured" assignment, I recommend the zeallot package by Nate Teetor.