Some Neat New R Notations

August 22, 2017
By

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The R package seplyr supplies a few neat new coding notations.


abacus

An Abacus, which gives us the term “calculus.”

The first notation is an operator called the “named map builder”. This is a cute notation that essentially does the job of stats::setNames(). It allows for code such as the following:

library("seplyr")

names <- c('a', 'b')

names := c('x', 'y')
#>   a   b 
#> "x" "y"

This can be very useful when programming in R, as it allows indirection or abstraction on the left-hand side of inline name assignments (unlike c(a = 'x', b = 'y'), where all left-hand-sides are concrete values even if not quoted).

A nifty property of the named map builder is it commutes (in the sense of algebra or category theory) with R‘s “c()” combine/concatenate function. That is: c('a' := 'x', 'b' := 'y') is the same as c('a', 'b') := c('x', 'y'). Roughly this means the two operations play well with each other.

The second notation is an operator called “anonymous function builder“. For technical reasons we use the same “:=” notation for this (and, as is common in R, pick the correct behavior based on runtime types).

The function construction is written as: “variables := { code }” (the braces are required) and the semantics are roughly the same as “function(variables) { code }“. This is derived from some of the work of Konrad Rudolph who noted that most functional languages have a more concise “lambda syntax” than “function(){}” (please see here and here for some details, and be aware the seplyr notation is not as concise as is possible).

This notation allows us to write the squares of 1 through 4 as:

sapply(1:4, x:={x^2})

instead of writing:

sapply(1:4, function(x) x^2)

It is only a few characters of savings, but being able to choose notation can be a big deal. A real victory would be able to directly use lambda-calculus notation such as “(λx.x^2)“. In the development version of seplyr we are experimenting with the following additional notations:

sapply(1:4, lambda(x)(x^2))
sapply(1:4, λ(x, x^2))

(Both of these currenlty work in the development version, though we are not sure about submitting source files with non-ASCII characters to CRAN.)

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