Variable assignment with zeal!
zeallot allows multiple or unpacking assignment in R. With zeallot you can tighten code with explicit variable names, unpack pieces of a lengthy list or the entirety of a small list, de-structure and assign object elements, or sample all of these at once.
zeallot isn't pushed to CRAN yet, because we want your feedback. If you aren't familiar with downloading packages from GitHub (it's possible!) we'll quickly touch on how to install zeallot.
- First make sure you have the devtools package installed,
install.packages('devtools')- Next use the devtools function install_github to install this package,
devtools::install_github('nteetor/zeallot')- Make sure zeallot was successfully installed,
library(zeallot) # No error? You're good to go!zeallot defines a %<-% operator to perform unpacking assignment. The operator
expects a list, or nested list, of bare names on the left-hand side and a vector
or list of values on the right-hand side.
Because R won't allow us to separate our bare variable names using commas we use colons instead.
library(zeallot)
a: b %<-% c(0, 1)
a
#> 0
b
#> 1If you are unfamiliar with multiple, parallel, or unpacking assignment, all we are doing is condensing multiple lines of variable assignments into a single variable assignment line. Neat! If you are familiar, strickly speaking, zeallot only implements unpacking assignment.
In that first example we unpacked a vector of values, if we want to unpack a list of values we wrap our variable names with a set of braces, but otherwise little else changes.
{agenda: today} %<-% list('TODO: ..', Sys.Date())In the above example we save today's date to today. With a little elbow
grease, we can extract the year, month, and day from the today variable.
{agenda: today} %<-% list('TODO: ..', Sys.Date())
year: month: day %<-% strsplit(format(today, '%Y~%m~%d'), '~')[[1]]We have the year, month, and date, but using de-structuring we can avoid some of
the overhead. The %<-% operator will take our Date object and de-structure it
into a list of three elements, year, month, and day.
year: month: day %<-% todayAnd if we didn't need the year value we could skip it using the special name,
..
.: month: day %<-% today%<-% de-structures the Date object because there were three variable names on
the left-hand side of the operator; three variable names for the three
de-structured elements. If we specified two or four names, we would get an
error.
year: month %<-% today
#> Error: too many values to unpack
year: month: day: hours %<-% today
#> Error: expecting 4 values, but found 3Date objects (and other obejcts) are not always de-structured. A list of Date objects is still a list of values we can assign to individual names.
{today: tomorrow} %<-% list(Sys.Date(), Sys.Date() + 1)In reality we know we are not always dealing with flat lists. Fortunately, we can unpack nested values by nesting our variable names.
{{a: b}: {c: d}} %<-% list(list(1, 2), list(3, 4))
a
#> 1
b
#> 2
c
#> 3
d
#> 4So long as the structure of the variable names mimic the structure of the values, we can unpack values at any depth.
We could also choose to save the entire first tuple and only unpack the values of the second tuple.
{a: {b: c}} %<-% list(list(1, 2), list(3, 4))
a
#> list(1, 2)
b
#> 3
c
#> 4This is where I will conclude the README for now.
If you are intrigued by any of what is above I highly suggest you read through the introductory vignette. This README hopes to get your attention, but the vignette focuses on walking you through and teaching you all of zeallot.
Inspiration for this package goes to Paul Teetor.
Without his encouragement nothing would have gotten off the ground.